An explosion at a shipyard owned by STX Offshore & Shipbuilding in Changwon, South Gyeongsang Province, South Korea, has resulted in the deaths of four workers.

The incident occurred at around 11:37am on Sunday inside a 74,000t oil tanker that was under construction at the shipyard, reported Korea Times.

The workers were painting the inside of one of the carrier's 12m-deep tanks at the time of the blast, which resulted in smoke coming out of the vessel for between 20 to 30 minutes.

Firefighters from the local Changwon Fire Station were called to control the situation and were able to retrieve the bodies of the workers from inside the tank at around 1:30 pm.

The victims were identified as employees recruited by a subcontractor company of STX.

Authorities are currently carrying out an investigation to establish the cause of the explosion.

"The incident occurred at around 11:37am on Sunday inside a 74,000t oil tanker that was under construction at the shipyard."

A firefighter was quoted by Korea Times as saying: “We will cooperate with police to look further into the cause of the accident and the scale of the damage.”

The authorities confirmed that no other casualties were found during the incident.

The affected ship was docked around 250m from the shipbuilding plant's front gate at the time of the incident, and is expected to be delivered to Greek shipping company Andriaki Shipping by October.

STX noted that one of the project's three safety maintenance managers had cleared the commencement of the painting job that morning following the completion of normal preparatory procedures.

The company also stated that no inflammable-related job was carried out on the premises at the time of the blast.