A 29-year-old man died on an Old Port sidewalk Thursday night, and a witness said the man may have overdosed on heroin.

Police have not released the name of the victim, who was described as a transient, but said his death at 111 Commercial St. is not considered suspicious. The cause of death will be determined through toxicology testing by the state medical examiner’s office, said police Lt. James Sweatt.

A witness at the scene said friends of the man said he likely overdosed on heroin.

Charlie Berg, 39, was at a concert on the Maine State Pier with his wife earlier Thursday night. As the couple headed back to their car, they saw a group of people hauling the body of a young man onto the sidewalk.

Berg, a former emergency medical technician, said he rushed over to the man and took his pulse. Berg said the man’s pulse was strong and consistent at first, but disappeared completely within seconds.

“Several friends said that they had been with him, and they knew it was heroin,” Berg said. “They were almost a little, like, eerily calm. Like EMS were going to show up and deliver Narcan and they would be on their way.”

A few moments later, Portland EMTs arrived and took over, Berg said. Neither Berg nor Sweatt knew whether emergency personnel gave the man Narcan, an antidote to opiates that stops the effects of an overdose.

Berg said he watched for about 20 minutes as medical personnel worked on the man, but with no success.

The body of the man lay on the sidewalk until a hearse from a funeral home arrived.

Berg said he was shaken up by the episode, which lasted about an hour.

Sweatt declined to comment further on the man’s death, saying it was still under investigation.