British Transport Police (BTP) is responding to a train derailment near Wickford, Essex
The force says there are no reported injuries, and reports "the rear carriages of a train derailed in an upright position" at 14:12 BST - here's BTP's statement in full
An image from the scene shows the train having come off the tracks
National Rail says major disruption is expected "until further notice"
Investigators have been deployed to the scene to begin gathering evidence
It comes a day after a separate train derailment in Lewes, Sussex - the cause of that incident is still being investigated
Images show air ambulance crews landing in a field near the derailed train in Wickford, Essex.
British Transport Police said earlier there were no reported injuries.
Stay with us for the latest updates.
Image source, No credit
Image source, No credit
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Anna Johnson
BBC East
An eyewitness tells me people were "in shock" at the scene of the derailment.
He says groups of people have already gathered in the area in response.
"A couple of people were in shock," the man says, speaking anonymously.
"No one was off the train when I was there - the train was just off the track.
"I was quite shocked. It's not something you see every day, or you hear about often - especially on the UK railway."
As a reminder, a train also derailed near Lewes, East Sussex, yesterday.
Network Rail is now saying that major disruption is expected to continue "until further notice".
Earlier it had said delays would continue until 18:00 BST.
We'll continue bringing updates - including when services may resume - as this incident unfolds.
Inspectors from the Rail Accident Investigation Branch (RAIB) have been sent to Wickford.
"RAIB has deployed a team of inspectors to the site of a passenger train derailment at Wickford, Essex to begin gathering evidence," the organisation says on X.
Services between Wickford and Southminster, which is on a different line to London Liverpool Street, are also affected.
National Rail says the situation is "under investigation" and all services between Liverpool Street and Southend Victoria will be cancelled.
"Major disruption is expected to continue until further notice," it repeats.
Train operator Greater Anglia is urging passengers on the affected route not to travel until further notice.
But asked by one user on X if rail replacement buses will be running, it says there is no such plan at present.
Today's derailment is the second where a train has come off the tracks in two days, after yesterday's incident near Lewes in East Sussex.
Two people were seriously injured in that incident, but are not in a life-threatening condition, police have confirmed.
You can find out more about that developing story on our colleagues' live page here.
British Transport Police tell us its officers are attending with both paramedics and the fire service.
"Officers are currently on scene just south of Wickford railway station in Essex following reports that the rear carriages of a train have derailed in an upright position at 2.12pm today.
"We’re responding alongside paramedics and the fire service. There are currently no reported injuries."
We can now bring you a picture from the scene near Wickford in Essex.
The train has come off the railway tracks but remains upright.
Nobody has reported being injured at this stage, the British Transport Police says.
More from them shortly.
Image source, Toon Gambit/XNetwork Rail has just confirmed to us that a train has derailed.
"We are dealing with a derailment incident in Anglia, [region] and we are working quickly to understand the situation and to provide assistance where needed," a spokesperson says.
"We will provide further information in due course.”
Katy Austin
Transport correspondent
I understand British Transport Police are responding to reports of a partially derailed train in Essex.
All services between Southend Victoria and London Liverpool Street are cancelled, according to Greater Anglia's website.
Image source, Greater AngliaWe can now bring you the full statement issued by National Rail.
"There is a problem currently under investigation between Southend Victoria and Wickford, meaning that all lines are blocked.
"As a result, trains running between Southend Victoria and London Liverpool Street will be cancelled.
"Major disruption is expected to continue until approximately 18:00."
National Rail is warning there will be "major disruption" on services between Southend Victoria and London Liverpool Street this afternoon.
It says delays will continue until at least 18:00 BST.
A Greater Anglia train has derailed near Wickford in Essex, the BBC understands.
We'll bring you more as we get it.
