Sadiq Khan faces an anxious wait to find out if Londoners have re-elected him after Labour sources reported a lower than expected turnout at polling stations.
Around 1,500 local government workers will oversee the counting process from 9am Friday morning but the final result will not be known until Saturday at the earliest.
Opinion polls gave Mr Khan a commanding lead over Conservative rival Shaun Bailey although the gap narrowed in recent weeks.
A combination of Covid fears and a lacklustre campaign are likely to be blamed for a low turnout.
“While we are hopeful Londoners have chosen to re-elect Sadiq as their mayor, we remain concerned that turnout combined with voters believing they can afford to put smaller parties first without consequence, means it is not impossible that the Tories sneak over the line”, said a London Labour source.
Vote counting, using electronic machines is taking place at three election hubs - Alexandra Palace, Excel and Olympia
Ballot papers from half of the 14 London Assembly constituencies will be counted on Friday
Votes from the remaining seven will be left untouched until Saturday
Social distancing and other Covid safety measures mean the counts will be far slower than in previous elections.
The winner will serve a three-year term at City Hall after the election scheduled for May 2020 was postponed by the pandemic.