Lifeguards on Kauai reported surf of 25 feet as a northwest swell peaked Friday.
Kauai County officials officials closed all north shore beaches from the Hanalei Pavilion to Kee Beach to swimming because of the high surf.
A high surf advisory for Kauai County, Oahu, Molokai and Maui has been extended until 6 p.m. Saturday.
National Weather Service forecasters said surf should reach 15 to 20 feet Friday night, declining to 10 to 15 feet Saturday. West shores should see wave faces of 10 to 14 feet Friday night, going down to 8 to 12 feet Saturday.
The Coast Guard and National Weather Service warned beachgoers to be aware of the potentially dangerous conditions.
The Coast Guard said the public should use "extreme caution" on or near the ocean and heed the advice of lifeguards.
"When in doubt, don’t go out," the Coast Guard said in a news release.
National Weather Service forecasters said beachgoers can expect strong breaking waves and shorebreak. Rip currents can also make swimming difficult and dangerous.
On Thursday, an 18-year-old woman was swept into the ocean from a North Shore beach and nearly drowned, according to an Emergency Medical Services report.
She was swept off the shoreline by a large wave at about 11:30 a.m. at Ke Iki Beach, the EMS report said.
She was awake and breathing when paramedics took her to the hospital in serious condition.