Passengers suffering disruption because of a huge improvement programme at Britain's busiest railway station faced extra misery on Tuesday after a points failure and partial derailment caused chaos.
South West Trains (SWT) tweeted that the delays were caused by a "points failure/operating incident" near London Waterloo.
It said all services would be disrupted all day after a "low speed partial derailment" between Waterloo and Vauxhall stations, in which a passenger service collided with a Network Rail engineering wagon.
Delayed passengers tweeted pictures of the SWT service leaning against the wagon and resting at an angle on the tracks, with men in high-vis uniforms standing close by.
London Ambulance Service said it had checked over three people, adding: "Thankfully they did not need to go to hospital."
The points failure is stopping SWT from using one of five lines into and out of the station, National Rail said.
It said "major disruption" between Waterloo and Vauxhall stations was expected until 1pm.
In a joint statement, Network Rail and SWT warned passengers not to travel.
They said: "There are no injuries to passengers or staff and a very limited service is running to and from Waterloo, which is expected for the rest of today.
"The incident happened as the train was pulling away from its platform at Waterloo at 5.40am.
"An investigation to establish the cause of the incident is under way."
Meanwhile, a train at London's King's Cross Station hit the buffers on platform nine.
Staff in high-vis overalls were gathered around the front of the train, the 5:13am service from Royston, and a cordon was in place.
Network Rail said there was a "slow speed buffer collision" at around 6:20am and two people suffered minor injuries.
There is no expected service disruption as the crash was "very minor" the spokeswoman said.
The British Transport Police (BTP) said it was called to Waterloo at 6.04am.
Commanding Inspector Sean McGachie said: "There were very few passengers on board and no injuries have been reported.
"BTP is working with industry partners to investigate the circumstances and manage the situation with a view to returning Waterloo station to normal working as quickly as possible."
It comes after a freight train partially derailed close to Ely, near Cambridge on Monday afternoon.
Greater Anglia trains suspended services between Bury St Edmunds and Peterborough and said track repairs would likely take several days.
A spokeswoman for Great Northern said the Rail Accident Investigation Branch had been informed about the collision of one of its trains with the buffers at King's Cross.
A screen was later put up at platform nine which hid the front of the train, as staff - including police officers - gathered around.
Natasha Coella, 36, was on the train - the 0513 from Royston to King's Cross - having boarded at Stevenage, and told the Press Association: "We just all went flying.
"It's as if while we were slowing down it kind of accelerated again."
She said she feels as though she has pulled her collar bone, adding she could see a few injuries, but nothing major.
"No one expected it, and people just went from one end of the carriage to the other," she said.
Ms Coella said passengers could see smoke at the front of the train when they disembarked.
A spokesman from Great Northern said: "At 6.20am this morning a Great Northern train came into contact with the buffers at low speed at King's Cross Station.
"The Rail Accident Investigation Branch has been informed."
A small protest of less than a dozen people from the RMT Union congregated outside King's Cross Station.
In another incident, passengers were evacuated from Holborn station in the capital's West End amid reports of a fire.
The Central Line's Twitter account said the station was closed "while we respond to a fire alert".
It said trains were initially being held at the station while a "faulty train" was inspected.
Several people posted on social media that they heard bangs, followed by smoke and panic.
User Sophie Walker posted: "Holborn station evacuated, there's smoke and people are crying and freaking out ..."
Al Gwatkin, 43, from Chelsea, was getting off the Piccadilly line to transfer on to the Central line at Holborn when the incident happened.
"All of a sudden everyone came running out saying 'they've evacuated the station'.
"You don't know if it's terrorist-related. You're just like 'oh my God, get out of here'. There was panic down there. People were screaming," he said.
A member of staff outside the station said there had been a problem with a train and emergency services were investigating.
Two fire engines, a police van and an emergency response unit were parked outside the station.
A member of staff from London Fire Brigade, who emerged from Holborn station and left in one of the parked fire engines, said the issue was caused by a piece of equipment that had become overheated.
He said he would expect the affected train to move off shortly.
Holborn station later reopened.