PERTH, Australia — Two women have been injured by a humpback whale while swimming with the giant mammals off the northwest Australian coast, media reported on Tuesday.

A 15-meter (50-foot) mother whale was protecting her calf when she swam at a group of snorkelers and swung her tail at Ningaloo Reef near the town of Exmouth on Saturday, Nine Network television reported.

A 29-year-old woman was struck by the tail and sustained fractured ribs and internal bleeding, Nine said.

She and was flown to a Perth hospital on Sunday and remained in a serious but stable condition, the WAtoday website reported.

The second swimmer was struck by the same whale's pectoral fin, which tore the swimmer's hamstring, Nine reported.

The Western Australian state government licenses tour operators and sets conditions including keeping swimmers a safe distance from whales that they observe.

The government's Department of Biodiversity, Conservation and Attractions said it was working closely with the industry and the tour operator involved to understand how the incident occurred.

"Swimming with humpback whales involves some inherent risk," a department statement said.