Three people are feared dead after going missing in different parts of the River Thames.
Police are searching the water in Shadwell Basin, under Waterloo Bridge and a stretch of the river in Kingston.
It comes as hundreds took to the water to cool off as temperatures soared above 30C on Tuesday.
A man, believed to be aged 22, was swimming with friends in Shadwell Basin, Wapping, and did not resurface.
Police officers including a marine policing unit and other emergency services were at the scene.
The marine policing unit were also trying to find two other people at different locations in the river.
Scotland Yard said the second person went missing in the water by Waterloo Bridge and a third near Kingston High Street.
Police were called to 18:06 Shadwell Basin to a report of a man seen to enter the water just after 6pm.
At 8:30pm officers were called to near Waterloo Bridge. Shortly after, at 8.35pm, more officers attended at Kingston, after reports another man was seen in the river.
Elsewhere in the UK, emergency services found the body of a man in a lake at Cotswold Water Park in Cirencester.
He had been reported missing at about 1.40pm.
