Three gunman dressed in all black stormed a birthday party on the edge of downtown Miami and opened fire early Monday, shooting 12 people and causing a chaotic scramble as they tried to flee, authorities said.

Three of the wounded were hospitalized in critical condition, police spokesman Det. William Moreno said. Another person fleeing the home was struck by a vehicle and was in stable condition. Police are searching for the suspects.

The men opened fire with automatic weapons around 12:45 a.m. One AK-47 and two pistols were found. It was unclear if the shooting happened in the home or outside what authorities described as a block party.

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Police had roped off about four blocks with yellow tape in the area of the shooting, located in Miami's Overtown neighborhood, a run down area in the shadows of downtown's glistening skyscrapers. Crime scene trucks were parked along the street as detectives searched for a motive. Shell casings were sprayed across the road and inside the home, some possibly from Fourth of July celebrations, authorities said.

A total of 100 rounds were fired at four or five different locations, Miami police Chief John Timoney told FOX News.

Timoney said they believe one of the guests at the party was the intended target.

"They clearly had one intended victim and they sprayed the crowd," he told FOX. "People fled the scene in panic."

He dismissed concerns the shooting was gang related.

"We're leaving everything open," he said. "My sense is we should bring this case to a close sooner rather than later."

Miami Fire-Rescue spokesman Ignatius Carroll said initially there were so many victims that there were not enough ambulances to take them to the hospital.

"There were a couple hundred people running around outside, running for cover because there was still shooting in the area," he said.

Styrofoam cups and paper plates littered the street next to shell casings. Birthday signs were left behind, and residents came out of their homes to talk about the shooting.

Rose Godbolt MacFarland, 58, lives in a house on the corner of the street where the shooting took place. She said there were more than 100 people at a birthday party.

Shortly after the shooting, eight people crowded in front of her porch and begged to come in for shelter.

"It was like an army out here," she said.

After she let all the kids inside, MacFarland said she padded one young man down for fear he, too, was armed. He was alert and talking, the blood streaming down his side. She stayed with him until an ambulance arrived.

"My niece said he might be the gunman," she said. "But I was saving somebody's child."

The Associated Press contributed to this report.