It is not yet known if the incident was an explosion or an implosion, according to port sources.

The port's Newton King Tanker Terminal has been closed to all shipping since Tuesday morning's explosion aboard the 5965-tonne Singapore-registered Perla ripped a 2m-long hole in the methanol tanker deck. No-one was injured in the incident, which was the first of its kind in the 24-year history of petroleum exports from the terminal.

Liquigas general manager Mike Bolger is reported as saying storage levels - of 2000 tonnes at Christchurch and 1300 tonnes at Dunedin - are down, but there is no immediate likelihood of the South Island running out of LPG.

However, he hoped the damaged Perla could soon be moved from the terminal to allow other vessels, including the Boral Gas which has been waiting off port since Tuesday, to berth and load the much-needed LPG. The Boral Gas is due to load 1300 tonnes of product for Dunedin.

Off-spec methanol from the Perla is being loaded into road tankers to allow temporary repairs at the port. The Perla is then scheduled to go to either Nelson or Lyttelton, where the remained of the methanol will be discharged, before she heads overseas for full repairs.

The Maritime Safety Authority is investigating the cause of the accident.

Jon Hacon, manager of port services firm, Westgate Transport, said it was thought the methanol cargo would be finished unloading and the ship cleared in around 72 hours.