Seven workers were killed by an explosion during installation work on a platform in Delta State, Nigeria on Tuesday.

The workers were killed as a ladder was being installed at the Benin River Valve Station in Gbetiokun in OML 40 on 7 July, state player Nigerian National Petroleum Corporation (NNPC) said.

The work was being carried out by a contractor of Nigerian Petroleum Development Company (NPDC), a subsidiary of NNPC. NPDC operates the facility on behalf of the NPDC/Elcrest joint venture.

All other personnel who were working on the platform at the time of the explosion have been accounted for.

London-listed Nigerian independent Seplat Petroleum Development, which is an indirect stakeholder in the facility's joint venture operator, said in a statement on Thursday that the fire was quickly extinguished and that no Seplat employees were involved.

"The explosion occurred during the installation of a ladder on a platform at the Benin River Valve Station which is used for exporting Gbetiokun production. The site of the incident is some distance from field operations on OML 40, which were unaffected," Seplat said.

Seplat subsidiary Eland is a 45% stakeholder in Elcrest, with the other 55% held by Starcrest.