Up to 500 black youths, angered because police broke up an outdoor party, roamed the Liberty City neighborhood in northwest Miami early this morning, hurling rocks and bottles, setting trash fires and looting a gas station, authorities said.

Police said the violence apparently was triggered when they ordered some of an estimated 1,200 to 1,400 youths dancing in African Square Park to turn down their radios, and some rocks and bottles were thrown.

After the incidents spread into the street, police in riot gear cordoned off a 30-block area and urged motorists to stay out of Liberty City, the predominantly black community where race riots in 1980 left 18 persons dead.

Several people in a car passing through the area were injured by rocks and bottles thrown through the windows, police spokesman Antonio Roberts said, adding that shots were reported fired at police. By 2 a.m., 19 arrests had been reported.

Miami police spokesman Juan Santos said a gas station was set afire, and some police cars were reported damaged. Santos said the neighborhood appeared to be quieting down around 2 a.m.

The disturbance occurred about 25 blocks from the black Miami neighborhood of Overtown, which was torn by two days of lootings and burnings last December after a police officer shot a black man in a video-game parlor.