Two people were dead and more than a dozen others were injured from gunfire and vehicles hitting fleeing revelers at a Michigan party over the weekend, police said.

As police were about to break up the roving outdoor party in Saginaw just after midnight Saturday, gunfire broke out, with indications that multiple shooters were involved, Michigan State Police said.

"Detectives later determined at least five different caliber weapons were used in the incident," the agency said in a statement.

The dead, not publicly identified, were described as a 19-year-old man and a 51-year-old man. At least 13 others were injured in the attack. Information about their conditions was unavailable, police said.

It wasn't clear which victims were struck by gunfire and which were hit by vehicles as they fled. No suspects were in custody, and no descriptions were available.

State police said the party was promoted on social media and had been broken up at other locations earlier that night. Officers had staged nearby and were preparing to repeat the action, the agency said.

The gunshots were preceded by a fight among partygoers, state police said, and suspects may have fired defensively but indiscriminately into the crowd in response to initial shots.

The violence remained under investigation Sunday.