City lifeguards will keep shark warning signs up at Makaha Beach until at least this morning as a precaution after a shark attack Wednesday afternoon near shore.

A 51-year-old woman who had been swimming about 250 yards offshore sustained a large gash across her right arm, shoulder and torso in the attack. Lifeguards, assisted by surfers, brought her to shore at about 2:30 p.m. Paramedics treated the injured woman on the beach and transported her to a trauma center in serious condition.

After the rescue, lifeguards posted shark warning signs and cleared the water. The beach was reassessed Thursday, with lifeguards patrolling the area. No shark was spotted Thursday in the Makaha Beach area, said Shayne Enright, spokeswoman for the city Emergency Medical Services.

Wednesday’s incident was the fifth shark attack in the state this year, and the first on Oahu in 2016. Three occurred on Maui and one on Kauai this year, and none involved a fatal injury.

The last shark attack at Makaha Beach occurred in late October when a boy on a bodyboard was bitten on the leg about 50 to 60 feet from shore.