A contractor suffered burns to his face and arms in an explosion at a water treatment plant north of Upper Hutt today.

A Fire service spokesman said the explosion, at Te Marua water treatment plant, happened at 3.30pm.

Greater Wellington Regional Council's communication manager said the blast happened while two electrical contractors were working on a switchboard.

The other contractor escaped injury but the burnt man was taken to hospital.

Mr Sangster said there was a small fire but that was brought under control.

"The power is currently off at the Te Marua water treatment plant and we're expecting to have electricity restored at midnight.''

He said the incident would not affect the water supply for the area.

Police and the regional council would investigate the incident.

"We're an organisation that takes workplace health and safety extremely seriously, so we'll be looking at this to find out what happened and to make sure we've got processes in place to stop it happening again,'' Mr Sangster said.

- APNZ