Statoil is still investigating the cause of a mystery power failure that has paralysed its Visund A platform in the Norwegian North Sea.

The facility was reported to have been shut-in on Sunday after the outage at around 15:00, with 84 of its workers subsequently airlifted by helicopter to the nearby Gullfaks A platform.

Some 44 workers remained on Visund to tackle the issue and Statoil also planned to fly specialists out to the platform on Monday in an effort to restore operations at the field, a spokeswoman told Stavanger Aftenblad.

She subsequently informed Upstream that the cause of the power failure had not yet been ascertained and it was still not certain when production would restart.

The semi-submersible accommodation, drilling and processing platform has been producing at an average rate of 12,000 barrels per day of oil and 47.3 million cubic metres per day of gas.

Oil is sent by pipeline to Gullfaks A for storage before offloading to tankers while gas is exported via the Kvitebjorn pipeline to the onshore Kollsnes processing plant.

Statoil operates the field with a 53.2% stake, with partners Petoro (30%), ConocoPhillips (9.1%) and Total (7.7%).