A worker died in an ammonia leak Wednesday night at a Stavis Seafoods warehouse where chemical fumes were so strong that Boston Fire Department hazmat crews initially could not reach him, officials said.

The victim was not identified. He was found on the second floor of the facility near a stairwell, Fire Chief of Operations John Walsh said.

Firefighters and officials in yellow hazmat suits swarmed the entrance to the warehouse, described in a Tweet as a “very large cold storage facility’’ on Channel Street.

The overwhelming smell of ammonia prompted street closings, and local business people and residents were ordered to stay in place, or stay away from area.

The leak was reported just before 6 p.m., the end of a shift for employees at the warehouse, where the chemical is used in the refrigeration process, officials said.

In a statement, Stavis Seafoods chief executive Richard Stavis said the company is devastated by the death of the worker and grateful that others got out safely.

“We were devastated to learn that one of our warehouse employees has died as a result of the ammonia leak at a Stavis Seafoods warehouse,’’ the statement said. “We are thankful that four employees who were in the building at the time were able to quickly and safely evacuate.’’

The company would not release any information about the worker until his family had been notified, the statement said.

“We want to understand exactly what happened and will of course cooperate with all authorities in their investigation,’’ Stavis said.

The worker was pronounced dead at the scene, said Steve MacDonald, a Fire Department spokesman said at the scene.

“It’s obviously a tragic incident,’’ MacDonald said.

Firefighters initially tried to rescue the victim but could not reach him,

“They made a valiant effort, but they were pushed back by the ammonia,’’ MacDonald said.

Crews had trouble accessing the building because of the overwhelming smell, Walsh said. But firefighters were able to shut off the main valve and stop the ammonia leak shortly after 9:20 p.m., officials said.

MacDonald said that investigators were working to determine the cause of the leak. Employees indicated that the building holds about 5,300 pounds of ammonia, MacDonald said.

He said the investigation into the leak and death is being conducted by the Fire Department, the Boston police homicide unit, and Suffolk District Attorney Daniel F. Conley’s office.

Foul play is not suspected in the death, Police Commissioner William B. Evans said at the scene.

MacDonald said he was unsure whether there were prior safety issues at the building, though he was not aware of any.

Officials from the state medical examiner’s office, who will conduct an autopsy on the victim, arrived on scene shortly after 9 p.m.

Firefighters and the hazmat crew remained on the scene late into Wednesday. “We’re going to be here awhile,’’ Walsh said.

Firefighters first responded just before 6 p.m. to a report of the leak at the company’s warehouse, located at 7 Channel St., the department reported in a Tweet.

A level 3 hazmat situation soon was declared, meaning that any firefighter entering the cold storage facility had to wear “fully encapsulated suits on air,’’ the department tweeted.

“Firefighters unable to make entry to the area where the ammonia shutoff is. This is a very large cold storage facility,’’ the department tweeted.

Boston police issued a traffic advisory stating that parts of Summer and D streets were closed to traffic. Motorists and pedestrians were asked to avoid the area, the department wrote in a Tweet.

Olivia Arnold can be reached at olivia.arnold@globe.com. Travis Andersen can be reached at travis.andersen@ globe.com. Follow him on Twitter @TAGlobe. Rachel Riley can be reached at rachel.riley @globe.com.