Updated at 2:15 p.m.

Lawrence Mayor Dan Rivera and Gov. Charlie Baker said a gas leak reported early Friday morning in Lawrence was an isolated incident and is no longer a public health threat. At a press conference Friday afternoon, they said that most evacuated residents would be able to return home at 3 p.m.

Earlier Friday morning, Rivera had urged residents of a neighborhood bordering the Merrimack River to evacuate their homes as emergency responders raced to shut down a major gas leak in the area.

The evacuations came one year after dozens of homes in Lawrence and neighboring towns were leveled by fires and explosions caused by massive gas leaks.

This time, the gas leak did not cause any explosions or fires, public officials said, and electricity and gas will be turned back on for those who can return to their homes Friday afternoon. The only people who will not be allowed to return home at 3 p.m., Rivera said, are those who live on South Broadway and Carver Street, between Andover and Merrimack Streets.

Rivera also said Columbia Gas and public officials from across the state responded quickly to shut off gas and electricity service, and evacuate residents.

"I have a very critical eye when it comes to the work of Columbia Gas," Rivera said, adding that in this instance, the company reacted quickly and efficiently to protect the public and fix the problem.

Columbia Gas said it sent workers door-to-door to check for leaks in about 146 homes and businesses.

A spokesperson for Columbia Gas said Friday morning that new pipes installed after last year's explosions appeared to have developed a leak. The company was excavating near the St. Patrick's church on South Broadway, which was not affected last year.

"If you are in that area you should get out of your house," Rivera said Friday morning.

Jeff Hall, spokesperson for the Red Cross, said there were about 280 people — including families with young children and some elderly residents — at an emergency shelter set up in the Arlington Middle School's gymnasium Friday morning. Local community groups, Hall said, brought supplies to the shelter, and EMS and mental health professionals were on-hand for anyone needing medical attention.

"We're just trying to make everybody as comfortable as possible. We understand that nobody expected to be out of their homes," Hall said. "It's a bit of a chaotic situation, but we've been through this about a year ago," referencing the evacuations after last year's explosions.

Rivera said the shelter will remain open overnight for those who cannot return home Friday and for anyone who needs help. Public officials also urged residents to remain cautious and call 911 if they smell gas or fire.

First responders began evacuating homes in Lawrence in the pre-dawn hours, and utilities cut power to around 1,400 homes and businesses in the area.

“At approximately 3:15 a.m. this morning we got a call that we had a high pressure gas main leak," said Lawrence Fire Chief Brian Moriarty. "The gas was traveling the sewers. We had explosive range gas in a number of different areas in the Salem and South Broadway area.

“We started an emergency evacuation of all the residences and buildings in the area,” he said.

Rebecca Talavera of South Lawrence said she woke up in the middle of the night to the smell of gas and called the police, who told her to evacuate immediately. She and her infant son are now out of their home, which she said brings back bad memories. She also had to evacuate her home one year ago, shortly after she found out she was pregnant with her son.

"It's scary, the fact that we could have been sleeping and not even known," she said. "It could have been the same situation as last time."

Columbia Gas is pursuing a class-action settlement that would pay $143 million to about 175,000 residents and businesses in the region for impacts of the 2018 gas fires.

This is a developing story. Chris Burrell and Craig LeMoult contributed to this article.