A 68-year-old woman suffered a serious leg injury when she was bitten by shark while swimming offshore of Waikoloa this morning, the Hawaii County Fire Department said.

The woman was about 500 yards offshore of Anaehoomalu Bay when a shark attacked her about 8 a.m, fire officials said.

Hawaii Department of Land and Natural Resources officials said the captain of an ocean sports vessel reported the incident, after hearing calls for help coming from near a channel marker. They said the marker was about 600 feet offshore.

Officials said a tender from the Spirit of Aloha tour vessel was used to take the woman to shore, where she met by first responders who treated her lower-right leg injury and transported her to North Hawaii Community Hospital in Waimea.

The size of the shark is unknown, officials said.

A fire department helicopter flew over the area but its crew did not spot any sharks.

Shark warning signs were placed along Anaehoomalu Bay on the Kohala Coast and will remain in place until noon on Sunday, after HFD does another surveillance flight, DLNR officials said.