Waikiki lifeguards on Saturday closed one beach and posted warnings on several others because of an infestation of dangerous box jellyfish.

The shoreline at Hanauma Bay Nature Preserve was shut down. The city's Ocean Safety and Lifeguard Services Division had earlier estimated 2,300 jellyfish at Waikiki beaches and 1,000 at Ala Moana shores.

But the agency later downgraded those numbers to 300 and none, respectively.

The Hanauma Bay beach was to reopen Saturday night, and the warnings on the other beaches were set to expire before midnight.

The monthly influx of the jellyfish began Friday when lifeguards in Waikiki spotted about 400 of the critters.

Their name comes from the shape of their medusae. They carry powerful venom, thought to be among the most deadly in the world, that can instantly stun or kill fish and shrimp, and do great harm to human swimmers. They also are called sea wasps.

Warning signs about the jellyfish were posted at Ala Moana Beach Park, Diamond Head Beach Park, Duke Paoa Kahanamoku Beach Park, Kapiolani Beach Park, Kuhio Beach Park and San Souci Beach.