NEW YORK — A New York City firefighter died Sunday night after falling off an elevated span of the Belt Parkway in Brooklyn while responding to a car accident, authorities said.

Mayor Bill de Blasio identified the firefighter early Monday as Steven H. Pollard, 30, who joined the Fire Department about 18 months ago.

“It’s a very sad night here in our city,” the mayor said at a news conference Monday. “This is particularly painful because we’ve lost a young man serving our city as a firefighter.”

About 10 p.m., Pollard responded to the scene of a two-car accident in the westbound lanes of the Belt Parkway on the Mill Basin Bridge, said Daniel A. Nigro, New York City fire commissioner.

Pollard arrived on the eastbound span of the parkway, which is separated from the westbound span by a gap, Nigro said.

When Pollard tried to get from one side of the bridge, which had recently been rebuilt, onto the other to reach the crash — a car that had flipped over with two people inside — he fell more than 50 feet in the space between the two spans, Nigro said.

Pollard was taken to Kings County Hospital in Brooklyn, where he was pronounced dead.

“It’s a terrible loss for the department, to lose a member just at the beginning of his career like this is devastating to us,” Nigro said.

Two people rescued from the overturned car were also hospitalized, a Fire Department spokesman said. One was taken to the hospital in serious condition, and the other had minor injuries.

The gap on the Mill Basin Bridge that officials said Pollard fell through is surrounded by concrete barriers that are about 3 feet tall. The bridge opened to traffic in 2017, replacing a decades-old drawbridge that did not have a gap in place.

A construction worker at the bridge Monday said the space between the spans was a design feature of the bridge. From the gap, it is a 52-foot drop the ground below, which is mostly covered in sand.

It was not clear whether Pollard knew about the gap when he tried to cross from one span of the bridge to the other. Fire Department officials declined to discuss any specifics around firefighters’ response to the car crash or whether there were conditions that may have caused Pollard to fall. Nigro said the department was investigating the circumstances. A spokesman for the New York City Department of Transportation said it was working closely with the investigation.

Pollard was a rookie firefighter who joined the Fire Department in June 2017. He finished an 18-month probation period in December, a Fire Department spokesman said, and was assigned to Ladder Company 170 in Brooklyn.

Gerard Fitzgerald, president of the Uniformed Firefighters Association of Greater New York, a union representing city firefighters, said Pollard “made a massive impact in the Brooklyn community” during his short time on the job.

Pollard also came from a family of firefighters: his father, Ray, retired after more than 30 years as a New York firefighter, and his brother is an 11-year veteran of the Fire Department who is currently assigned to Ladder Company 114 in Brooklyn, the department said.

“This is a family that has done so much for New York City, and now they’re going through this loss,” de Blasio said. The mayor said he had ordered flags throughout New York City to fly at half-staff Monday to honor Pollard.

“He devoted his life to the people of our city, like his brother, like his dad, he was trying to do such a good and important thing,” de Blasio said. “It’s just a very, very tough loss.”

New York City Police Commissioner James P. O’Neill said on Twitter early Monday that his department sent its condolences to Pollard’s friends, family and colleagues. New York City “will never forget your sacrifice,” he wrote.

The last time a New York City firefighter was killed on duty was in March, when Michael R. Davidson, 37, died while fighting a massive blaze in a Harlem building being used as a set for a movie directed by Edward Norton.

This article originally appeared in The New York Times.