"Provisional statistics for 6 June show a 40 per cent increase in racist incidents, compared to the daily average this year, and a fivefold increase in the number of Islamophobic incidents," the mayor's office said in a statement.
It said 54 racist incidents were recorded yesterday, compared to a daily average of 38 so far in 2017.
Twenty of them were anti-Muslim incidents, well above the 2017 daily average of 3.5.
On his Facebook page, Khan called on Londoners "to pull together, and send a clear message around the world that our city will never be divided by these hideous individuals who seek to harm us and destroy our way of life".
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He also warned that "just as the police will do everything possible to root out extremism from our city, so we will take a zero-tolerance approach to hate crime."
The three attackers, Khuram Butt, Rachid Redouane and Youssef Zaghba, were then killed by police.
The Islamic State jihadist group later claimed responsibility.