A search is underway in Yellowstone National Park for a seasonal worker from China who went missing Thursday while swimming.

The park says that 21-year-old Feiyang "Isaac" Xiang of the Hubei province was backpacking with four friends. He disappeared while swimming in the Yellowstone River near its confluence with Hellroaring Creek in the park's northern section.

Xiang was swimming with two companions around 11:45 a.m. when he was pulled away from the shore by the current.

Initial search efforts Thursday afternoon did not turn up any sign of the seasonal concessionaire, who is about 5 feet 6 inches tall and 140 pounds.

Search efforts increased on Friday. Approximately 40 people including a helicopter, two dog teams, and 20 Yellowstone and Grand Teton National Park employees searched the Yellowstone River corridor.