Four men were shot — two of them left fighting for their lives — in three shootings overnight that Boston Police Superintendent William G. Gross told the Herald are not thought to be connected.

“Thank God everyone made it,” Gross said this morning. “There’s too many firearms on the streets.”

Mayor Martin J. Walsh said it was the most violent night in the city in the past six months.

“We’ve just got to stay diligent,” he said. “We ‘re not letting up. Occurrences like last night will happen.”

Boston Police spokeswoman Officer Neva Coakley said the first shooting happened at 10:28 p.m. on School Street in Jamaica Plain, and the last at 5:29 a.m. on Lawrence Avenue in Dorchester.

In Jamaica Plain Gross said, “A young man was in the back of a premises and he was approached by two individuals. Unfortunately, an altercation ensued and he was fired upon.”

Gross said the victim was in critical condition.

“In all hopes he’ll make it,” he said.

The next gunplay broke out at 12:28 a.m. when a man visiting “a companion” on Burrell Street in Roxbury was shot by an unknown suspect. He, too, is in critical condition, Gross said.

Approximately five hours later on Lawrence Avenue in Dorchester, one man was shot in the bicep and the other in the shoulder.

Their injuries are not life-threatening, Gross said.