Three people have died and six others have been taken to hospital after a train derailed in Aberdeenshire.
Aerial shots appear to show one carriage completely overturned after the service from Aberdeen to Glasgow Queen Street came off the tracks near Stonehaven earlier.
British Transport Police said formal identifications are yet to take place but the driver is believed to have been killed.
They added that his family has been informed and is being supported by specially-trained liaison officers.
Officers are working to inform the families of the other two people who died.
Aerial shots appear to show a carriage on its side and away from the tracks
Three people are confirmed dead after the derailment
Three people are confirmed to have died after the train derailed.
Six people have been taken to hospital with injuries which are not believed to be serious.
Sky correspondent Gerard Tubb, who is at the scene, said questions remain as to why it appears it took three hours for an emergency call to be made.
The train was a 6:38am service but emergency responders were not called until around 9.40am.
Prime Minister Boris Johnson has spoken with Scotland’s First Minister Nicola Sturgeon about the derailment.
Mr Johnson told reporters: “Clearly the most important thing now is that the British Transport Police, who are in charge of the investigation, find out exactly what happened and that we all work together with Network Rail, with everyone else who is responsible, to make sure we get to the bottom of this and that nothing like this happens again.”
He added: “I do think it’s a very good idea to look at the effect of substantial rainfall on all our vulnerable infrastructure everywhere.
“As I understand there was about a months worth of rainfall in a short period, which undoubtedly aggravated the problem there.”
Ms Sturgeon had earlier tweeted after the deaths were confirmed: “My deepest condolences are with the loved ones of those who lost their lives in this tragic incident.
“I have just been updated by Network Rail and the emergency services on the ongoing operation. My thanks go to them, and my thoughts remain with everyone affected.”
Footage posted on social media showed smoke billowing above trees surrounding the railway line.
A number of ambulances and emergency helicopters were pictured parked in a nearby field.
Rail industry sources told PA that the suspected cause of the incident was a landslip.
Smoke billows from derailed train
Three people are believed to have died after the train derailed
The train was said to have six carriages.
Twelve people – six passengers and six staff – were on board.
The Scottish Ambulance Service said they had deployed six ambulances, special operations response teams, an air ambulance, and patient transport vehicles.
The train reportedly derailed due to a landslip
Scottish Fire and Rescue crews were also in attendance, while coastguard teams were sent from nearby locations, along with a coastguard search and rescue helicopter from Prestwick.
British Transport Police Chief Superintendent Eddie Wylie said: “This is a tragic incident and first and foremost our thoughts are with the families and friends of those who have very sadly died this morning.
“We remain on scene alongside our emergency service colleagues, and a major incident operation has been underway. I would like to reassure the public that this was not a busy service, and from CCTV enquiries and witness statements we believe all passengers have been accounted for.”
Ambulances and emergency helicopters arrived at the scene
Emergency services are at the scene of the derailment. Pic: Lewis Michie
Smoke has been billowing from the area where the train derailed
Ms Sturgeon described the derailment of the ScotRail passenger train as an “extremely serious incident” earlier.
“I’ve had an initial report from Network Rail and the emergency services and am being kept updated,” she posted on Twitter.
“All my thoughts are with those involved.”
Speaking later during First Minister’s Questions in the Scottish Parliament, Ms Sturgeon said there had been “early reports of serious injuries” as she revealed a “major incident” had been declared.
Smoke has been billowing from the area where the train derailed
Smoke billowed above trees surrounding the railway line. Pic: Lewis Michie
Emergency service vehicles lined up near Stonehaven
Thunderstorms had caused flooding across Aberdeenshire on Wednesday, prompting the cancellation of some rail services and the shutting of a number of schools.
At 9.49am on Wednesday, Network Rail Scotland posted a video of a landslip and flooding on rail tracks at Carmont.
Smoke rising from the scene of the derailment suggested it occurred near to a bend in the tracks close to Carmont.
“At Carmont, we’ve had reports of a landslip, which means services can’t operate between Dundee & Aberdeen,” Network Rail Scotland had posted on Twitter.
It is unclear whether the landslip was directly related to the incident.
A police officer is seen walking along the track near to the scene where the train derailed
Commenting on the suspected reasons of the crash, Nigel Harris, the editor of Rail magazine, told Sky News: “Somewhere south of Stonehaven the driver – the weather was apparently appalling – he encountered an obstruction, a landslide, on the track and had to reverse his train and go back along the way he’d come.
“And then go onto his own line and head back north towards Aberdeen, at which point he ran into another landslide which had clearly happened after he had passed by in a southerly direction.
“That then caused this terrible incident.”
Local journalist Lewis Michie, speaking to Sky News from the scene shortly before 1pm, said there were “still a lot of emergency services arriving” at that time.
He described how the area could only be reached by a “very, very narrow” road, while the train line running through the area had “very, very steep” embankments.
“The issue here at the moment, it seems to me, is that this is possibly the most inaccessible area this could have happened,” he said.
He added: “This morning it was probably the worst flooding I have seen in the northeast for a long, long time.”
The site of the train derailment near Stonehaven
Prime Minister Boris Johnson said he was “saddened to learn of the very serious incident in Aberdeenshire and my thoughts are with all of those affected”.
Transport Secretary Grant Shapps said earlier: “The Rail Accident Investigation Branch are on their way to the scene at Stonehaven… We’ll find out more from them.
“There has been some very extreme weather and concerns about landslips.”
Train derailment ‘extremely serious incident’
Network Rail Scotland said they were “working alongside the emergency services to respond to an incident involving a train near Stonehaven”.
A spokesperson added: “It is too early to confirm the exact nature and severity of the incident and more details will be made available once known.”
Andrew Bowie, the Conservative MP for West Aberdeenshire and Kincardine, said he had spoken by telephone to Mr Shapps.
The local MP, who said a major incident had been declared at Aberdeen Royal Infirmary, had been in Stonehaven surveying flood damage earlier on Wednesday.
Mr Bowie told Sky News: “We had torrential rain in this part of the world last night.
“Stonehaven saw terrible flooding in the town centre, saw many roads closed off and water coming into houses and businesses.
“Obviously it’s too early to speculate as to whether that had an effect on what we’re seeing just south of here.
“But the area has been battered over the last 24 hours.”
He said the train derailment had occurred in an “incredibly rural area”.
“It’s an area of beautiful farmland, forests and it will make accessing the site incredibly difficult for the emergency services,” he added.
A spokesperson for NHS Grampian said: “We can confirm we are on a major incident footing following an incident involving a train near Stonehaven.
“We have well-rehearsed protocols and procedures for dealing with such incidents and are working closely with emergency service partners.”
The Rail Accident Investigation Branch, the independent investigator, said it was sending a team of inspectors to the site to conduct a preliminary examination.
Network Rail chief executive Andrew Haines was said to be cutting short a family holiday in Italy in order to visit the crash site on Thursday.
The last time a train crash caused a passenger or member of staff’s death in the UK was at Grayrigg, Cumbria, in February 2007.
Mick Lynch, the assistant general secretary of the Rail, Maritime and Transport union said: “RMT is aware of the major incident at Stonehaven and our reps are liaising directly at senior level with both Scotrail and Network Rail.
“Our priority at this time is to support our members, their colleagues and their families and to do all that we can to assist the rescue operation which RMT members are currently involved in.
“The facts behind this incident will need to be established in due course but at this stage we are focused on support and assistance and our thoughts are with all those impacted by this tragedy.”