Police are investigating gunfire that left one man seriously injured at around 2:16 a.m. Monday on the 100 block of Harvard Street, The Port.

A man, a 30-year-old Watertown resident, is in a Cambridge hospital with serious injuries that are not believed to be life threatening, said Jeremy Warnick, director of communications and media relations for Cambridge police.

More than 20 shell casings were found by police during a preliminary investigation, Warnick said, and at least two vehicles were seen fleeing the area after the reports of gunshots, which came from residents as well as the city’s ShotSpotter technology. There had been no arrests made as of 6:54 a.m., when police sent an email about the incident.

The fatal shooting of Xavier Louis-Jacques, 19, took place in North Cambridge on March 27; before that came two gunfire incidents in The Port on March 24 and 26, and March 2 saw one at Fifth and Spring streets in East Cambridge, leading to the arrest of two Boston men on drug charges. Before that round of incidents, the last such was Dec. 21 on Harvard Street near Davis and Portland street