Workers at a bridge construction project in Wellesley struck a gas main Friday afternoon, causing a leak that sent fumes into the air and temporarily brought commuter trains to a halt.

Crews for National Grid were still working hours later to try to cap the leak while maintaining gas service to customers, said Charlotte McCormack, a spokeswoman for the utility.

“Our number one priority is to get the gas turned off and make sure the area is safe,” she said. “Then we’ll clear the site and find out what the ramifications are — were they working inside or outside the markings.”

A strong smell of natural gas filled the area after the main was struck about 1:45 p.m. at the Rockland Street bridge project. Linden Stree was closed between Kirkland Circle and Route 9 east, and service was halted about an hour on commuter rail and CSX lines

A handful of people complained of headaches at a medical office building on Washington Street, but they declined treatment, according to police.

At In Pursuit of Beauty on Washington Street, Katelyn Haggerty and Helen An said the hair products being used masked any gas smell in the salon, and they didn’t realize anything had happened until a firefighter came in and checked to make sure gas levels were safe.

“I went outside to my car, and there was such a strong gas smell that I couldn’t put my windows down,” Haggerty said. “It was kind of weird because there were all kinds of men in uniforms all up and down the street, but we were all fine.”

The leak occurred in a 10-inch cast-iron gas main, said National Grid spokesman David Graves. The gas was blowing into the air, which Graves said is the best outcome in such situations. Danger of combustion is much higher when a gas leak occurs in an enclosed space, he said.

Wellesley Fire Captain David Marchetti said the leak occurred when a worker hit the main with a pile driver.

“As soon as it happened the workers smelled it and heard it,” Marchetti said at the scene.

He said residents in the area should know that “there are no hazardous conditions. We are waiting for the gas leak to be stopped and for it to be capped, and we are going to remain on the scene until that happens.”

By late afternoon, a faint odor lingered in the air.

Marcos Gusmao, a landscaper who said he was working in the front yard of a home on Linden Street all afternoon, said his crew smelled the gas, but no one felt sick.

“I saw ambulances and firetrucks going down to the bridge, but I was just focused on my job. No one was bothered,” he said.