A female snorkeler suffered "what appears to be an apparent shark bite" this morning while swimming off of Lahilahi Beach, about one mile south of Makaha Beach, said Bryan Cheplic, spokesman for the city's emergency services department.

The woman — described as being in her mid-40s — was taken to The Queen's Medical Center in serious condition with a wound to her forearm as police and lifeguards kept an eye on a shark that was swimming about 50 yards off shore.

A lifeguard on a Yamaha Waverunner and officers in the Honolulu Police Department's helicopter spotted what appeared to "be a very large shark approximately 16 feet in length" 10 minutes after the woman was injured, Cheplic said.

They tracked the shark for another five to 10 minutes before it swam out to deeper water, Cheplic said.

"Whether this was the creature that was guilty of the attack or not, we're not able to verify," Cheplic said.

Lifeguards cleared the ocean one mile in each direction and put up signs warning swimmers to stay out of the water, Cheplic said.

The woman was snorkeling in front of the Hawaiian Princess condominiums when she was injured around 8:45 a.m., Cheplic said. She made it to shore on her own and bystanders helped control her bleeding, he said.

"i want to thank the bystanders from the condo for acting quickly and for their quick thinking," Cheplic said. "They used towels and blankets to control the bleeding and saved her life, essentially."

Lifeguards will reassess the situation tomorrow before deciding whether to take down the warning signs, Cheplic said.