Around 18,000 homes in the Rossendale area of Lancashire were affected when a gas main ruptured on Monday.
Homes in Bacup, Waterfoot, Rawtenstall, Newchurch and Crawshawbooth have no gas and there is "no guarantee" it will be restored by December 25, according to a National Grid spokeswoman.
The ruptured gas main set light to an overhead power cable in Holme Lane, Rawtenstall, which knocked out electricity to 30,000 homes in the area.
United Utilities restored electricity supplies on Monday night.
A National Grid spokeswoman said: "We've still got 18,000 homes off gas but we have repaired the gas pipe supply and we expect shortly to be able to start the process of restoring gas to homes."
She said 200 engineers are poised to start the arduous process of going from house to house to restore gas supplies.
The National Grid spokeswoman said: "We can't say how long it will take us to get 18,000 properties back on."
She said National Grid could not promise to restore supplies by Christmas Day: "At this stage we can't make that promise. We are doing everything we can. We'll be working round the clock."
The spokeswoman said members of the public should ask engineers to show identification before letting them into their homes.
