Staff and contractors have been evacuated from Northport and the neighbouring Marsden Point oil refinery after a tsunami alert was issued in the wake of a major earthquake off the Kermadec Islands on Friday morning.

The refinery lies at the mouth of Whangārei harbour and usually produces about 70% of the country’s fuel. It is also the main supply point for Auckland, with half its output being delivered directly to Auckland via an underground pipeline to Wiri.

The Civil Defence alert was issued after the magnitude 8.1 quake struck about 8.30am off the islands about 1,000 kilometres north-east of Auckland. It followed an earlier 7.4 quake around about 6:40am. 

The latest update places the risk of tsunami down Northland’s west coast from Cape Reinga to Ahipara and down the east coast to Whangārei. It also takes in Great Barrier Island and the eastern Bay of Plenty and East Cape, from Matata round to Tolaga Bay.

Much of the rest of the country’s coast is at risk of tidal surges and unusual currents.

A tsunami from the south-west Pacific would usually be expected within one and three hours, according to the National Emergency Management Agency.

Plant shut

No emergency shutdown was required at the refinery as processing was halted late last month for a four-week maintenance shutdown. 

The site, including extra contractors on site for the shutdown, was evacuated in line with the company’s emergency response plan, a spokesperson said. She was unable to say how many people had been on site at the time.

The refinery lies right on the coast. Its potential vulnerability to a tsunami has long been recognised, although the site is shielded by Bream Head from the worst impact from an event from the Kermadec trench.

A 2017 assessment of risk to the country’s fuel infrastructure noted a 4.8 metre wave was likely in a one-in 500-year event, rising to about 7.5 metres in a one-in 2,500 year return period event.

That report noted that full fuel tanks were less at risk from damage and that little damage was likely in the event of a one-metre wave. Modelling showed there would always be damage from a seven-metre wave.