It is understood the offshore Maui A production platform "tripped" early Wednesday morning, cutting gas supplies to shore via the sole pipeline.

Field owner Maui Development Ltd later confirmed the shutdown, saying it believed the shutdown had been caused by problems that occurred while testing a safety device on the platform. Attempts were then made to restart the platform, but neither of the facility's two generators were able to be started.

Field operator Shell Todd Oil Services later restarted the platform, and gas flows resumed from, it is believed, mid-afternoon. MDL said major gas users were kept updated about the situation throughout the day.

Methanol manufacturer Methanex was probably hardest hit by the shutdown as it is this country's largest gas user and one of the closest big users to the Maui facilities.

Contact Energy's peaking New Plymouth power station might have also been affected and, to a lesser extent, its Auckland Otahuhu A and B plants, though not the Stratford TCC plant which uses Tawn gas. Genesis Power's Huntly station might have been forced to switch to coal.

The volume of gas already in the Maui pipeline, from Oaonui to near Huntly, plus gas from other fields, principally Kapuni, should have been sufficient to ensure small industrial, commercial and residential users were not affected.