GALVESTON, Texas—An outdoor rap concert ended in multiple fights and unruly partying that police say “completely overwhelmed” officers who struggled to restore order and herd nearly 5,000 cars off the beach in this island city.

At least 12 people were arrested and one officer broke his finger Sunday trying to control the crowd, Galveston police Lt. Jorge Trevino said. Almost four hours passed before police cleared the streets.

Problems began when police tried arresting a group of men fighting. Other fights then broke out and left four officers patrolling the concert “completely overwhelmed,” Trevino said.

All on-duty officers and some whose shifts had not begun were eventually called to the scene, Galveston police Sgt. Byron Franklin said.

Authorities shut down four city streets while trying to get as many as 5,000 cars off East Beach, he said.

“It was an absolute fiasco,” said Johnny Smecca, owner of Mario’s Italian Restaurant.

Smecca said he saw people urinating in the alley behind his restaurant and dancing on top of cars.

The concert, called the “Spring Break Party Beach Bash,” was hosted by Houston radio station Party 93.3.