Sadiq Khan has condemned those responsible for a suspected terror attack on Tube train at Parsons Green and said: "London will never be defeated".
Horrified rush hour commuters fled the District Line train after an explosion sent a "heatwave" through packed carriages injuring 18 people.
Scotland Yard confirmed they were treating the blast, which happened around 8.20am, as a "terrorist incident" as a bomb squad were rushed to the scene.
The Mayor of London said in a statement: "Our city utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life.
"As London has proven again and again, we will never be intimidated or defeated by terrorism.
"I am in close contact with the Metropolitan Police, Transport for London, Government and other emergency services who are responding at the scene and leading the investigation."
Mr Khan confirmed that he will attend an emergency COBRA meeting in Whitehall with Prime Minister Theresa May this afternoon before praising the capital's emergency services in the wake of what is believed to be the third terror attack in the capital this year.
"My sincere gratitude goes to all our courageous emergency responders and the TfL staff who were first on the scene," he added.
"I urge all Londoners to remain calm and vigilant, and to check TfL’s website for travel advice."
At least 18 people were injured when a "shot of flames" reportedly swept packed carriages, London Ambulance Service confirmed.
A spokesman added that none of the injuries are believed to be serious or life-threatening.
One passenger told the Standard she saw a lady who appeared to have been burnt and a man with "a wound on his head".
Another witness said they have "never been so scared in my life" while images emerged of traumatised commuters outside the station.
Armed police and 50 firefighters descended on at the station which has been cordoned off by police.
All trains are suspended between Earl's Court and Wimbledon as emergency services deal with the incident.