Paramedics took at least two men to the hospital after incidents amid high surf on the North Shore on Wednesday.

A man in his 20s was in critical condition after he was spotting waving for help in the ocean at Sharks Cove. Lifeguards on personal watercraft rescued him, performed CPR on the sled behind the watercraft and revived him, according to an Emergency Medical Services report.  He was brought to shore at Waimea Bay and taken to the hospital at about 4:15 p.m.

At 12:51 p.m., paramedics took a 23-year-old man to the hospital in serious condition after he got into trouble at Sunset Beach.

Paramedics took a third person, a 55-year-old man, to the hospital in critical condition after he suffered cardiac arrest at Sunset Beach at about 1:23 p.m. It wasn’t clear if his condition was related to the surf.

Surf on the North Shore was estimated at 15 to 20 feet Wednesday and is expected to remain in that range today.

The National Weather Service has extended a high surf advisory for north and west shores of Oahu, Kauai County and Molokai until 6 a.m. Friday. The advisory is also in effect for north shores of Maui and west shores of the Big Island.

Surf along north-facing shores is expected be 10 to 15 feet today. Surf along west-facing shores is expected to hit 10 to 14 feet today.

West shores of Hawaii island can expect  5- to 8-foot surf.

A third swell is expected to arrive Saturday and the advisory could be extended into the weekend.

Forecasters warn beachgoers can expect strong breaking waves, shorebreak, and strong longshore and rip currents making swimming difficult and dangerous.

People going to the beach should heed advice given by lifeguards and exercise caution, the National Weather Service said. Boaters should also expect recreational surfers utilizing harbor channels to reach surfing areas.