Lifeguards are warning beach-goers on the north shore to be aware of “dangerous” surf.

Paramedics took two people to the hospital who got into trouble in the surf at Waimea Bay, Emergency Services Department spokeswoman Shayne Enright said.

Paramedics treated a 23-year-old woman who went to the hospital in serious condition at about 11:45 a.m. A 14-year-old boy also went to the hospital in stable condition at about 1 p.m.

“Waimea Bay is extremely dangerous,” Enright said. “We are seeing 10-foot shore break, extremely hazardous conditions. Long intervals add to the hazards and we are seeing 30 minute breaks (between sets).”

Lifeguards have also taped off the Sharks Cove and Three Tables area to beach-goers.

Surf is building to heights of between 12 and 20 feet along north-facing shores of all islands and 10 to 15 feet along west-facing shores due to a northwest swell, the National Weather Service said.

A high surf advisory is in effect for the north and west-facing shores of all islands until noon Tuesday, when it will become a high surf warning until 6 p.m. Wednesday, according to the National Weather Service.

Waves are expected to reach heights of 25 feet on north shores and 20 feet during the peak of the swell Tuesday night and Wednesday.

A small craft advisory has also been issued until 6 a.m. Tuesday.