The department did not give the cause of the blast. Korean media reports said a tank exploded in a ship under construction.
The four men, aged in their 30s to 50s, were painting the ship in the yard in Jinhae, an industrial hub on the country’s southeast coast, an official from the National Fire Agency said.
“No additional injuries were reported,” the official said.
The ship is intended to carry about 74,000 tons of oil, and to be delivered to a Greek buyer in October.
On May 1, a crane collapsed at shipyard of Samsung Heavy Industries, killing six people and injuring more than 20.