LAWRENCE — Thousands of residents across Merrimack Valley could remain without heat or hot water well into December, as the recovery effort from the Sept. 13 disaster is weeks behind in the race to return gas service to homes before the onset of cold weather.

On Friday, Massachusetts officials and executives at Columbia Gas set a new target of Dec. 16 to have service restored to all of the 8,400-plus customers affected by the gas fires and explosions, nearly one month beyond the original deadline. They urged those residents to seek alternative housing as winter and the holidays near.

“In many cases it will be the safest option, given the cold temperatures, until you can return home,’’ Governor Charlie Baker said Friday morning, adding, “This ongoing recovery process has been difficult and challenging’’

Columbia Gas officials said they will deploy more than 2,000 workers by next week, including 1,400 plumbers, gas fitters, electricians, and inspectors inside people’s homes and businesses. That’s triple the number inspecting homes at the outset of the recovery effort.

Joe Albanese, a construction industry executive and former Navy commander tapped to lead the recovery, said the plan now is to postpone installing new appliances and instead see if existing fixtures still work safely enough to provide heat and hot water. That would cut down on the upfront work, Albanese said, and allow the utility to return later and replace all appliances.

“Each day that goes past our deadline is a day too long,’’ said Albanese. “As temperatures drop we recognize there’s an incredible sense of urgency to get people back into their homes with heat and hot water. We are racing against the winter.’’

The National Transportation and Safety Board has tentatively identified the trigger for the Sept. 13 incident as an errant sensor that allowed high-pressure gas to overwhelm local networks. One person was killed, two dozen people were injured, and thousands were immediately evacuated until gas to individual homes was shut off.

So far, nearly 7,000 people are in alternative housing provided by Columbia, including trailers set up in local parks. But many have been reluctant to leave their homes, and the extension of the deadline Friday cause further alarm.

Yuleidy Tejada is worried about her mother-in-law. She is in her 60s, on medication, and has no heat or hot water.

Tejada fears that the extension of the deadline will cause further stress, as cold weather arrives, but her mother-in-law does not want to stay in a faraway hotel.

“You can’t just pick up and go to a hotel,’’ she said.

Jim Wefers, in his 80s and retired, and his wife, Mary, have waited out the weeks since the disaster in their North Andover home so that they can be there when inspectors arrive. They get by with space heaters and takeout food.

But, Wefers said, the later deadline will cause them to reassess their situation, especially as November and Thanksgiving approach.

“You want to stay in your house, you want to protect your house, know what’s going on,’’ he said. But, he added, “the heat’s our concern.’’

The recovery work is taking place in the streets and inside properties. The street work is moving fast, as Columbia has replaced most of the 45 miles of pipes damaged by the disaster, as well as many of the service lines to individual properties. The inside work, though, is moving very slowly, as workers have encountered outdated systems and housing conditions.

Pablo Vegas, chief recovery officer for Columbia gas parent NiSource Inc., said that close to a third of the 8,400 metered customers who lost service may not have heat and hot water heading into December. So far, service has been restored to just over 1,000 customers.

Vegas promised residents more frequent updates and mailings, and said the utility will hold open houses for residents on Saturday.

“I just want to say that I get it . . . we understand this has been an incredibly frustrating process for everybody,’’ Vegas said.

Leaders of the three communities — Lawrence, Andover, and North Andover — called on Columbia to make written commitments that include better communications and prompt response to claims, repair of all roads dug up during construction, and a promise to replace all appliances in homes once service has been completely restored.

Mayor Daniel Rivera of Lawrence initially demanded that all appliances be replaced. But he said he received assurances from the state fire marshal’s office that appliances that can be repaired can be relit safely. The difference could mean seeing a heating system repaired in three hours, rather than the current three days to install new appliances in old houses.

“We have to realize this plan is really about safety, getting people in their home with heat and hot water,’’ Rivera said.

Milton J. Valencia can be reached at milton.valencia@globe.com. Follow him on Twitter @miltonvalencia.