The leak was reported by Transport for London on Wednesday (March 22) after the A4 Bath Road was closed.
National Grid, which operates the gas infrastructure, has apologised to residents for the inconvenience caused while work is carried out.
A statement from National Grid said: “We are currently carrying out essential gas mains repairs on the A4 Bath Road.
“This work needs to be done to help ensure properties in the area keep on being supplied with safe and reliable gas supplies for cooking and heating.
“We're sorry for any inconvenience the work may be causing.
“Our current estimated completion date for the work is Tuesday, March 28.”
The closure is causing delays around Cranford, including The Parkway heading up towards the M4 and Great South West Road.
Drivers have been urged to take the A312 to the M4 Heathrow Spur junction for Heathrow Airport.
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