About 700 homes in north London have spent the night without a gas supply and are waiting to see if they will be reconnected by Christmas.
Residents in the East Barnet area lost the service in the early hours of Sunday.
A spokeswoman for National Grid said water from a burst main had got into the gas pipes, cutting off the flow.
About 3,000 cooking and heating appliances have been distributed to all affected households.
The damaged gas main has been located and repaired and the process of pumping the water out of the gas system has begun.
Residents who have enquiries about the loss of gas supply should call 0845 605 6677
Paul Hanafin, National Grid's Incident Controller, said "At present it is too early to say when gas supplies will be restored.
"We are drafting in engineers from as far as the North Midlands to help and we are working hard to ensure that residents have their gas back as quickly as possible.
"We appreciate that this is a difficult time for residents, but we ask them to bear with us as we work to resolve this situation".
An incident room has been set up in St Mary's Church of England Primary School in Little Grove and National Grid is working with Hertfordshire Council's emergency planning department to identify vulnerable people within the area.
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