Sadiq Khan has called for Londoners to "stand guard" against any rise in hate crime following the EU Referendum decision.
The Mayor of London was joined by Met Police chief Bernard Hogan-Howe to warn xenophobic attacks would be met with "zero tolerance".
Reports of racial tension in the capital have increased following Thursday's vote to leave the EU, with A Polish cultural centre in Hammersmith daubed in racist graffiti over the weekend. Khan and Hogan-Howe say police will be "extra vigilant".
In contrast to the final decision, London voted overwhelmingly to remain in the EU: just five of the 33 boroughs wanted to leave.
In a statement, Khan said, "Last week the country voted to leave the European Union but London voted to stay. In every corner of our city, including those few areas where the majority voted to leave, people of all nationalities, races and religions live cheek by jowl, in harmony.
"I say to them all — you are, and you will continue to be, welcome in London and in all our communities.
"As mayor, I take seriously my responsibility to defend London's fantastic mix of diversity and tolerance.
"So it's really important we stand guard against any rise in hate crimes or abuse by those who might use last week's referendum as cover to seek to divide us.
"I've asked our police to be extra vigilant for any rise in cases of hate crime and I'm calling on all Londoners to pull together and rally behind this great city. While I'm mayor, addressing hate crimes will be a priority for the Met. We will have a zero tolerance approach to any attempt to hurt and divide our communities."
Mr Khan also added it was important not to "demonise" the 1.5 million Londoners who voted for Brexit.
"While I and millions of others disagreed with their decision, they took it for a variety of reasons and this shouldn't be used to accuse them of being xenophobic or racist. We must respect their decision and work together now to get the best deal for London," he added.
Met chief Sir Bernard added, "London is a diverse global city where people from many different backgrounds live and work side-by-side in safety. That hasn't changed in the past few days but if people do have any concerns they should let the police know. We will investigate vigorously any reports or crime motivated by hatred."
Figures show around 850,000 Londoners were born in EU countries other than the UK; many are concerned about what Brexit will mean for their futures.