Two hospitals east of London have asked patients to stay away after their emergency departments were hit by floods on Sunday.
Whipps Cross is powerless and removes 100 patients and Newham Hospital is asking patients to use other A&E emergency services.
Ambulances are being re-directed after the flood caused severe flooding in homes, roads and stations.
The London Fire Brigade says it has taken more than a thousand flood-related calls.
It rescues people trapped in cars and helps those with flooded basement and collapsed roofs.
A spokesman for the Barts Health NHS Trust, which manages both Newham and Whipps Cross hospitals, said: “Patients are being asked to go to other hospitals where they can. A major incident has been called to the entire Trust.”
Many of the capital’s roads were closed due to flooding, including the Blackwall Tunnel, A12 and parts of the North Circular.
The Stepney Green station is still closed even though eight other Station and London Overground stations are open.
A yellow storm warning is always available in the southeastern parts of England.
St James’s Park in London saw 41.6mm (1.6in) rainfall on Sunday, making it the wettest part of the country.
Residents on a street in Woodford, east London, have taken buckets, brooms and wooden boards to prevent rising rainwater from flooding their homes.
The manager of the restaurant, Maria Peeva, said her neighbor’s bedroom was flooded and that her son had helped others protect their homes from the floods.
Ms Peeva, 46, told PA news: “My son went to buy food at a local store – by the time he came back the whole road and the road was already flooded and water was entering our front door.