The driver of a train that derailed in Aberdeenshire is believed to have died, with the PA news agency reporting that there are fears of a second fatality.
Emergency services are responding to the "extremely serious" incident near Stonehaven after being called to the scene around 9.40am on Wednesday.
Footage posted on social media showed smoke billowing above trees surrounding the railway line.
A number of ambulances and a medical helicopter were pictured parked in a nearby field.
Rail industry sources told PA that the suspected cause of the incident was a landslip.
The train involved was said to be the 6.38am Aberdeen to Stonehaven service, made up of a locomotive and four carriages.
Twelve people – six passengers and six staff – were on board.
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The Scottish Ambulance Service said they had deployed six ambulances, special operations response teams, an air ambulance, and patient transport vehicles.
Scottish Fire and Rescue crews were also in attendance.
Scottish First Minister Nicola Sturgeon described the derailment of the ScotRail passenger train as an "extremely serious incident".
"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.
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.
Local journalist Lewis McKay, speaking to Sky News from the scene shortly before 1pm, said there were "still a lot of emergency services arriving".
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."
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 he had held an urgent meeting with rail operators about the Stonehaven derailment.
"British Transport Police & Network Rail are on location, along with rail workers who were nearby," the UK cabinet minister posted on Twitter.
"The UK Government will provide every support. My thoughts are with those involved and their families.
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 WednesdayRead More – Source