A fight or argument was reported at 2:47 a.m. in the 27000 block of Tyrrell Avenue, and as officers were en route to the area, police received more calls about possible gunshots from the same area.
Officers arrived to find the victim suffering from at least one gunshot wound. He was taken to a local hospital where he was later pronounced dead, police said.
The name of the victim, a Hayward resident, is being withheld until family members are notified of his death.
No arrests have been made in connection with the shooting. No suspect information was immediately available this afternoon, and investigators have not established a motive for the killing.
The shooting was the 13th homicide in Hayward in 2010.