Insurers and business are waiting to hear the cause of damage to the country’s largest gas pipeline to see if business interruption clauses are triggered.

Industries in the North Island, including the major food processors around Auckland, had gas supply stopped last Monday when the 307km Maui Pipeline was shut down because of a gas leak.

About 5000 businesses are estimated to have been affected.

The failure forced the Fonterra dairy company to dump around $NZ20 million ($15 million) of milk the day supply was cut, and dairy farmers had to pour out milk that it could not process.

Hospitals deferred elective procedures, three crematoriums had to stop operations and food manufacturers, hotels and cafes were out of action for a few days.

The pipeline took most of last week to repair, with supply increasing gradually as the operator, Vector, used back-up lines and rationed use.

The pipeline is thought to have ruptured because of erosion, but brokers and insurers contacted by insuranceNEWS.com.au say they are waiting for confirmation of the cause. This and policy wordings will determine whether a business interruption claim is triggered.

Disruption to supply was often excluded from insurance contracts at the time the pipeline was commissioned 30 years ago, but this clause has been dropped over the years as insurers became comfortable with the risk.