About 600 homes in north London are without heat in freezing conditions after a loss of their gas supply.
Some people in the East Barnet area lost the service in the early hours of Sunday.
A spokeswoman for National Grid said water from burst main had got into the gas pipes, cutting off the flow.
She said it was too early to say how long it would take to fix but some affected residents have been given fan heaters and electric boiling rings.
Residents who have enquiries about the loss of gas supply in East Barnet should call 0845 605 6677
The damaged gas main has been located and repaired and the process of pumping the water out of the gas system will begin later.
More engineers are being drafted in to help restore gas supplies, the National Grid spokeswoman said.
An incident room has been set up in St Mary's Church of England Primary School in Little Grove.