Authorities in a coastal New Jersey community activated a curfew Saturday night after thousands of people flocked to the beach on the hottest day of the year.

Authorities said the overwhelming size of the crowds that were amassed in the afternoon threatened public safety on the New Jersey shore. Multiple fights reportedly broke out, leading to a “public safety emergency” and a 9:00 p.m. curfew for Long Branch.

At the end of the night, the police arrested 9 people, four minors and 5 adults, in connection with fights.

Thousands of young people traveled to the beach by train to attend a “pop-up party” advertising on social media, city officials said.

The chaos peaked overnight as police officers from various agencies responded to the beach community and attempted crowd control. Officers with helmets and carrying shields were deployed.

Tensions rose when police used to smoke “in response to fights taking place and throwing bottles and rocks where the crowd did not disperse,” the county attorney said.

Not long after 9:00 pm, the police had closed off the area and most of the crowds had left the area. Countless bottles and other trash were found strewn on the beach after Saturday’s party.

The county attorney said a police car was vandalized, but no other damage or injuries were reported. Saturday’s commotion comes after last summer’s beach frenzy that forced Long Branch to postpone its July 4 fireworks display.

The curfew was scheduled to lift at 5:00 a.m. on Sunday.