Local resident Oriana Evans said she and her son helped casualties who were led off the train towards the community centre at Lewes, showing them where to go, including some passengers who were on holiday.

“I walked and chatted to some of them in shock really,” the 54-year-old jewellery maker said.

“They were in the carriages that rolled over.”

She said they told her they were alright but “really bruised”.

Other residents could be seen outside their homes in front of lines of emergency service vehicles and walking down to the community hub with chairs for casualties to sit on.

A bus was parked up by the hub awaiting for passengers to board, as well as taxis and one passenger could be seen being taken away in an ambulance.

A major incident has been declared following the train derailment near Lewes in East Sussex, British Transport Police (BTP) said.

Three carriages derailed onto their side, leaving a number of people trapped on board the Southern train, which was travelling from London Victoria to Eastbourne.

They have now been safely evacuated, the force said.

“At this time we believe that two patients have sustained serious injuries and a further nine patients have sustained less serious injuries,” BTP said.

“Patients have been assessed and treated at the scene, with some transported to local hospitals.

“Officers are continuing to respond at the scene alongside colleagues from Sussex Police and the local Fire and Rescue and Ambulance Services.

Assistant Chief Constable Ian Drummond-Smith said: “We’ve declared a major incident and a significant emergency service response is ongoing at the scene, but all passengers on the train have now been safely evacuated from the service.

“Our thoughts are of course with everyone affected, and I’d like to reassure the public that we’re supporting the Rail Accident Investigation Branch to establish exactly what’s happened. We’ll provide further information as soon as we are able”.

The MP for Eastbourne has said that it is “utterly shocking” to see the scenes following the derailment this afternoon.

Posting on Instagram, he wrote: “I’m full of gratitude for our emergency services who have responded quickly and are pulling out every stop to ensure that passengers and staff who were on the train are taken to safety as soon as possible - thank you to them.”

South East Coast Ambulance have confirmed that "two people sustained serious injuries" during this afternoon’s derailment.

The service said that there were about 150 people on board the train when it derailed near Lewes.

A spokesperson said: "We can confirm that two patients have sustained serious injuries and a further nine patients have sustained less serious injuries.

"Patients have been assessed and treated at the scene, with some transported to local hospitals for further treatment and care.

"A number of passengers who did not require hospital treatment have been taken to a local community centre, where they are being supported by partner agencies."

It added that it continues to respond to the major incident alongside other emergency services and urged people to avoid the area.

Fire engines, ambulances and police have been stationed along Landport Road in Lewes, East Sussex, where a community centre is hosting passengers from the derailed train.

Yana Ludwig, who was travelling alone on the train from London to Lewes, told reporters the experience as “completely terrifying”.

“There was a banging. Everything just went topsy turvy,” the 56-year-old from the United States said.

“It seemed like a really long time but it probably was 10 seconds of that before the carriage actually fell on the side.”

She described being propped up over the top of another passenger.

She added: “I’m pretty banged up.”

The graduate student thinks it was 20 minutes before the emergency services arrived, adding it seemed like a difficult place for them to reach.

She said everyone in the train was checking their fellow passengers were OK, adding: “These moments everybody kind of pulls together.”

East Sussex Fire and Rescue Service says it has sent 10 fire engines, a command support unit, technical rescue teams, officers and other resources to the scene.

A spokesperson said: "We have been helping reach passengers and assisting other emergency services."

University Hospitals Sussex NHS Foundation Trust has confirmed that it is currently responding "to a major incident" alongside other emergency services.

Meanwhile, Southern says it has requested rail replacement buses to run between Haywards Heath and Lewes.

They have not yet been confirmed, so passengers have been advised to continue using their own alternative routes.

There will be no service in either direction at Cooksbridge and Plumpton stations for the rest of the day, and anyone travelling to Gatwick Airport and connecting to a flight is being told to allow an extra two and a half hours for their journey.

The chaos caused by the train derailment will last until the end of the day, according to Network Rail.

A spokesperson for the group said: “A train has derailed in the Lewes area. This has closed all lines running through this station.

“As a result of this, trains are currently unable to run through the area to allow the emergency services to attend the incident.

“Major disruption is expected until the end of the day.”

Southern Rail has warned passengers not to travel.

A team of inspectors is at the scene of the crash, the Rail Accident Investigation Branch has said.

A spokesperson for the group said: “RAIB is deploying a team of inspectors to the site of a passenger train derailment near to Lewes, East Sussex, to begin gathering evidence.”

As disruption on the railway network continues, Southern Rail has issued a warning to passengers.

There are no services between Haywards Heath and Lewes and several other lines are experiencing severe delays.

Trains are also being cancelled between Brighton, Seaford and Eastbourne.

A spokesperson for Southern Rail said: “We strongly advise you DO NOT TRAVEL between Brighton, Lewes, Haywards Heath, Seaford and Eastbourne for the remainder of the day.

“No trains can run between Haywards Heath and Lewes. Trains between Brighton, Lewes and Eastbourne / Seaford are mostly cancelled.

“To allow you to travel, we have arranged for your ticket to be accepted on the below services at no additional cost.

- Southern services between Brighton and London Victoria - Thameslink services between Brighton and London Victoria. - Gatwick Express services between Brighton and London Victoria - London Underground between all London terminals.

Brighton and Hove Buses on the following routes: - 28 - Brighton (St Peter’s Church), Moulsecoomb (Brighton University), Falmer, Lewes (Post Office / Law Courts), Polegate, and Eastbourne

- 29 / 29B / 29X - Brighton (St Peter’s Church), Moulsecoomb (Brighton University), Falmer, Lewes (Post Office / Law Courts), Uckfield, Crowborough, Eridge, and Tunbridge Wells”