Polling stations across the capital are open from 7am today for the London mayoral and assembly elections.
The polling stations will stay open until 10pm.
Election organisers said the results will be declared at City Hall, despite the burst water mains on Sunday that flooded the building.
There are more than five million registered voters this year who will choose from ten candidates for mayor.
The frontrunners include the current Labour mayor Ken Livingstone, Conservative Boris Johnson and Liberal Democrat Brian Paddick.
The others candidates standing are Richard Barnbrook of the BNP; Gerard Batten of the UK Independence Party; Sian Berry of the Green Party; Alan Craig of Christian Choice; the Left List's Lindsey German; independent Winston McKenzie.
English Democrats candidate Matt O'Connor has withdrawn from the race but his name will still be on ballot papers as they had already been printed.
Vote counting will take place at Alexandra Palace, ExCeL and Olympia on Friday.
Once all the votes have been counted, the results for the Mayor of London and the London-wide assembly members will be announced at City Hall.
The constituency assembly member results will be announced as they happen in the count centres.