Boris Johnson has written a letter of support to New York mayor Michael Bloomberg as Americans came to terms with the damage caused by Hurricane Sandy.
The London mayor, who was born in New York, said Londoners stood "shoulder to shoulder" with the people of New York.
"As both a fellow New Yorker and a proud Londoner I am deeply saddened to see your great city under such pressure from Hurricane Sandy," he wrote.
"I am hugely encouraged by your response, that of public employees of NYC and indeed the response of emergency services and the American people up and down the east coast.
"Rest assured the people of London stand shoulder to shoulder with the people of New York at what is clearly an immensely difficult and challenging time."
Boris' words echo those of Tony Blair following the terrorist attacks of September 11 when he said Britain stood "shoulder to shoulder" with the United States.
President Obama declared a "major disaster" in New York state on Tuesday after Sandy hit the East Coast of the United States, leading to damaging floods and cutting power to millions of Americans.
At least 15 people are believed to have died in the US as a result of the storm, while around 80 people died as it moved through the Caribbean over the last week.