A violent hit-and-run crash that left a man lying dead on Morton Street early Saturday shook Mattapan residents, as investigators spent the day looking for the driver who fled the scene.

The 40-year-old Boston man was hit at 12:03 a.m. Saturday near the intersection with Fuller Street and was determined to be dead at the scene, according to law enforcement agencies.

The Massachusetts State Police and the Suffolk district attorney’s office did not identify the man Saturday.

“Whoever the person was, they didn’t even slow down. Look at the street — you don’t even see the skid mark,’’ said a 53-year-old man who would only give his name as Christian and said he saw the collision from his deck.

The impact knocked the victim about 30 feet down the street, he said. “They hit him and just kept pushing. That’s messed up,’’ the man said.

The man’s body was found in the right travel lane after the crash was reported in a 911 call, according to a statement from Suffolk District Attorney Daniel F. Conley.

Boston EMS performed life-saving attempts at the scene but were unsuccessful, said David Procopio, a State Police spokesman, in an e-mail to the Globe.

The vehicle that struck the man did not stop and continued west on Morton Street, police said.

Investigators were seeking a taxi driver they believe was a witness to the crash, according to the district attorney’s statement.

“The taxi driver is sought as a witness only and is not accused of any wrongdoing,’’ Conley said in the statement.

Witnesses told investigators that a white taxi cab was in the area around the time of the crash, the statement said.

Witness statements and video footage indicate the taxi cab was not damaged in a collision, and they are confident it was not involved in the crash, Conley’s statement said.

Earlier in the day, neighbors described a strong response by police and emergency crews who fought to save the man’s life.

Those who spoke to a reporter at the scene Saturday morning had to shout at times in order to be heard over the roar of traffic on Morton Street, which is a four-lane road.

Residents said they worry about their safety when they try to cross Morton Street, as vehicles often race down the roadway at 40 or 50 miles per hour through the heart of their neighborhood, Christian said.

Christian said he knew the victim, who had lived for about a decade in the neighborhood.

Nicole Toro, 21, said she heard what she thought was a car crash outside her home, and went outside to see a man lying on the street and what appeared to be a bystander pressing on his chest.

First responders arrived a short time later, she said, and they worked for about 15 minutes in an effort to resuscitate the victim. She knew he was dead when they stopped, stretched out police tape at the scene, and placed a sheet over his body.

“That was the first time I saw someone die in front of me,’’ she said. “His life just got taken away.’’

She said even with police and first responders at the scene of a fatal accident early that morning, traffic continued to drive at a high speed down Morton Street.

“One car rushed down the street’’ and past the crash scene, she said. “It was like, ‘slow down.’ ’’

Another man, who declined to give his name, said he was returning home at the time of the crash and saw a massive response by police and an ambulance crew.

Police were working Saturday to get a description of the vehicle involved in the crash, said Procopio.

John Hilliard can be reached at john.hilliard@globe.com.