A train has derailed at London Waterloo.
South West Trains (SWT) warned passengers to avoid the station and said it was dealing with an "operational incident".
Images showed the front carriage of a train leaning against a freight car, having apparently crashed into it.
London Ambulance Service said its paramedics had been called.
It said: "We checked over three patients following the train derailment at #Waterloo this morning. Thankfully they did not need to go to hospital."
London Fire Brigade said it was called at 6.12am to reports of an eight-car passenger train having collided with a freight train, but that no one was trapped or injured.
SWT said it was "a low speed, partial derailment".
It added: "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 underway.
"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.
"South West Trains and Network Rail are advising passengers not to travel."
British Transport Police said: "We are working with our industry partners to investigate the circumstances of the incident."
Separately, a points failure has further disrupted other services to the country's busiest rail station.
SWT said on its website: "There is a fault with a set of points on one of the lines approaching London Waterloo.
"This means that South West Trains are unable to use one of the five lines into and out of the station.
"This is expected to cause some delays to services, while trains use the available lines."
Disruption is expected all day, it said. The operator clarified on Twitter that the points failure was at a different location to the derailment.
London Waterloo is currently undergoing multi-million-pound expansion work to increase capacity.
A number of platforms are closed.
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