A shooting outside a market in western Massachusetts on Wednesday afternoon left a pregnant bystander on a passing bus in critical condition and her child dead after the baby was delivered at a hospital, the authorities said.

The shooting occurred during a dispute involving three suspects just before 12:40 p.m. at a corner in downtown Holyoke, Mass., a city of more than 37,000 residents about 90 miles west of Boston.

One stray bullet struck a public bus and the pregnant woman, who was seated inside, the authorities said. The woman, whose name was not released, was taken to a hospital in critical condition.

“The infant, who was delivered, and needed lifesaving medical services, tragically passed away,” the Hampden District Attorney’s Office said in a news release.

The three suspects were taken to area hospital and are in police custody, a spokesman for the prosecutor’s office said. The authorities did not immediately release their names, conditions or what injuries they had sustained.

The manager of a market near the site of the shooting said that one of the suspects had come into the store to buy juice.

“When he walked outside, two young boys waiting outside tried to jump him,” said Jose Almonte, who described all three suspects as young men in their early 20s.

Then, Mr. Almonte said, they struggled over a gun, and the suspect who was being jumped fired three shots.

Mr. Almonte said the episode had been captured by the store’s surveillance cameras, and that he was cooperating with the investigation, which is being handled by the Massachusetts State Police and the Holyoke Police Department.

The shooting happened less than two hours after Holyoke’s police chief, David Pratt, encouraged the public at a news conference to report shootings that happen in the city.

Gunfire detection technology installed throughout the city in March logged 113 incidents of gunfire from March through August, Chief Pratt said. The technology, called ShotSpotter, helps to detect and locate potential incidents of gunfire in a city.

“There were only 14 calls to 911 during this time frame for these gun incidents,” he said.

The Holyoke Police Department said in a Facebook post on Wednesday it had initially responded to a shooting in downtown Holyoke that day after receiving “multiple calls for help” and alerts from its ShotSpotter shooting surveillance system.

Mr. Almonte said that there is ample drug activity and other crime in the neighborhood.

“We’re in a country where the youth are killing each other,” he said.