Six weeks after three gas explosions and dozens of fires rocked the Merrimack Valley, thousands of residents remain without heat in their homes even as the weather turns cold.

Columbia Gas, the company believed to be responsible for the explosions, acknowledged that at least a couple thousand customers will be waiting beyond their original Nov. 19 deadline for full restoration of gas service.

"We are racing against winter," said Joe Albanese, the head of the restoration effort appointed by Gov. Charlie Baker.

“Our team is working around the clock to complete our mission of getting the affected residents home with gas service and back to normalcy as quickly and safely as possible,” Albanese added. “The set of circumstances created by this incident is unprecedented, and as part of this contingency operation, we are dedicated to continuously improving our repair process to achieve the shared goal of restoring gas service to customers. While we regret that some people will be delayed by a couple of weeks, we will keep working diligently to relight homes and businesses safely.”

On Sept. 13, an overpressurization in the gas lines occurred as crews were working to upgrade the system. A total of 7,772 homes and businesses lost gas service as a result of the incident, which killed 18-year-old Leonel Rondon and injured two dozen.

Lawrence Mayor Dan Rivera said his top priority is restoring heat and hot water to residents. He urged those without gas to seek assistance in finding alternative shelter.