Story highlights Four crew members were seriously injured in the explosion near the port of Himeji

The 64-year-old captain of the ship remains missing, authorities say

The tanker wasn't loaded with oil when the blast hit, the coast guard says

Ships and aircraft battled the blaze on the Shoko Maru, a 998-ton tanker

An explosion on an oil tanker off the Japanese coast set off a huge fire Thursday and left the vessel's captain missing.

Ships and aircraft battled the blaze on the Shoko Maru, a 998-ton tanker anchored about 5 kilometers (3 miles) off the port of Himeji in western Japan, the coast guard said.

Rescuers have recovered seven members of the eight-person crew, the coast guard said, but the ship's 64-year-old captain is still missing.

Four of the rescued crew remembers were seriously injured in the blast, the Himeji fire department said, and all seven of them were taken to hospitals after arriving in the port, which is about 75 kilometers (45 miles) west of Osaka on the Seto Inland Sea.

The tanker wasn't loaded when the blast went off Thursday morning, the coast guard said, reducing fears of a major environmental disaster.

Video footage showed water cannons dousing the stricken ship as large black plumes of smoke rose from a blaze roaring inside its body. Later images showed the tanker scorched, smoldering and listing to one side.

There was no immediate danger to other ships, as the tanker was located outside of the port facility, the coast guard said, adding that an exclusion zone was being set up around the damaged vessel.

The coast guard said it was still investigating the cause the explosion on the ship, which belongs to Shoho Shopping Co. Ltd, a company based in Hiroshima, Japan.