NEW YORK — Fire department officials continued to investigate the circumstances that led to the death of a rookie New York City firefighter Sunday night after he fell from a bridge in Brooklyn while trying to rescue two people involved in a car accident.

The firefighter, Steven H. Pollard, 30, died from injuries he suffered when he dropped more than 50 feet from the Belt Parkway’s Mill Basin Bridge onto heavy sand below, authorities said.

The city mourned Pollard’s death Monday. Dozens of firefighters lined the streets as his remains, draped in a flag, were carried from the city medical examiner’s office in Manhattan to a funeral home in southern Brooklyn. A procession of Fire Department vehicles escorted his body through the streets, passing firefighters who saluted or bowed their heads. Flags across the city were flown at half-staff.

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

Pollard had been with the department for about 18 months before his death. About 10 p.m. Sunday night, he was part of a crew of firefighters reporting to the scene of a two-car accident in the bridge’s westbound lanes, said Daniel A. Nigro, New York City fire commissioner.

Firefighters were dispatched to both sides of the parkway, according to a Fire Department spokesman. Pollard arrived on the eastbound span of the parkway, which is separated from the westbound span by a gap.

When Pollard tried to cross over the gap to get to the crash — a car that had flipped over with two people inside — he fell inside the space between the two spans, dropping more than 50 feet, Nigro said.

The firefighter was pronounced dead at Kings County Hospital Center in Brooklyn. The city’s medical examiner said Pollard died of multiple blunt impact injuries.

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

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 details of the incident or whether there were specific conditions that may have caused Pollard to fall.

The gap on the Mill Basin Bridge is nearly 2 feet wide and is surrounded by concrete barriers that are 3 1/2-feet high. The gap is a permanent feature of the bridge, which was opened to traffic in 2017, replacing a decades-old drawbridge. From the gap, it is a 52-foot drop to the ground below.

Glenn P. Corbett, a former assistant fire chief of Waldwick, New Jersey, who now teaches fire science at John Jay College of Criminal Justice, said that firefighters are trained on a range of scenarios for keeping safe while working on roadways. But at night, with poor lighting it may not have been obvious to firefighters that there were two separate spans on the Mill Basin Bridge, he said.

“It’s just one of those things that nobody realized,” Corbett said.

Nigro said Monday that the department was investigating Pollard’s death.

Pollard joined the Fire Department in June 2017 and finished an 18-month probation period in December, a Fire Department spokesman said. He 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 that 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 currently assigned to Ladder Company 114 in Brooklyn, the department said.

“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.”

Steven Pollard was the 1,151st New York City firefighter killed in the line of duty, officials said. The last death while on duty occurred 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.

Two people involved in the car accident Sunday night survived, a Fire Department spokesman said.

On Monday evening, firefighters gathered at Ladder Company 170 in Canarsie for a memorial service. Black bunting was hung around the station. Capt. James Quinn, the commander of the company, described Pollard as a laconic, hardworking and exacting man who loved his job.

“He was a good firefighter on his way to being a great firefighter,” Quinn said.

Quinn said Pollard had just passed his probation in December, and was to receive a patch with the number 170 to wear on his helmet in place of the orange patch worn by rookies. The new patch will now be given to his family at the funeral, the captain said.

This article originally appeared in The New York Times.