Digging at the site of the critical fuel pipeline was identified as an "exploratory" search for swamp kauri the day before the rupture happened, according to an industry insider with stories of the extraordinary wealth attached to excavating the buried logs.

Northland's Milton Randell was driving past the site of the pipeline rupture near Ruakaka, just south of Whangarei, last Wednesday, saw the earthworks and believed he was seeing the signs of a swamp kauri hunt.

Randell has 40 years experience in digging swamp kauri out of the ground and would be one of the most experienced to have worked in the industry.

His immediate impulse was to think it was a swamp kauri site - the same detail the NZ Herald was provided by a source familiar with the response to the rupture of the nation's only fuel line to Auckland.

The damage has put the pipeline out of action for 10-14 days and is causing severe disruption to flights in and out of Auckland Airport. Jet fuel can't be transported by road leaving airlines operating on reserves or having to fill up elsewhere.

"Like they had been digging around for a log - that's what it looked like," said Randell, 77, who currently runs Milton's Vintage Bulldozers & Tractors museum in Kerikeri.

"I saw they had been digging there and that's what I thought they were doing.

"If they were doing an exploratory dig, they might have hit the pipe and not said anything."

Randell remembered seeing it on Wednesday as he travelled past it on a trip from Kerikeri to Rotorua.

When he returned to the site yesterday - Sunday afternoon - he saw diggers and trucks gathered in the same area. He saw the area again on the evening news and that was when he learned the critical fuel pipeline to Auckland had been ruptured.