An operation is under way to put out a fire on a Russian fishing ship on Friday. (South Korean Coast Guard)

This photo shows rescued Russians on Friday. (South Korean Coast Guard)

ULSAN -- A Russian fishing boat carrying 25 people caught fire off the southeastern coastal city of Ulsan early Friday, leaving four of them missing, Coast Guard officials said.

The 769-ton vessel was carrying 100 tons of seafood in waters off Ulsan, about 300 kilometers southeast of Seoul, toward Russia when the fire broke out at 12:43 a.m., the officials said. All crew members were Russian.

After receiving a distress call, the Coast Guard sent rescue ships to the scene, but four crew members went missing.

The other 21 were rescued, 19 of them without any injuries. Two sustained minor injuries.

With the aid of Navy ships, authorities are continuing efforts to search for the four missing people and put out the fire. (Yonhap)