Three shearers in a Hawke's Bay woolshed are about to smash a world record.

James Mack, Eru Weeds and Luke Mullins are half-way through their challenge to sheer 1347 sheep in eight hours.

So far, they've got through 804 in four hours.

A team of World Sheep Shearing Society judges is overseeing the event, at Waitara Station, northwest of Napier.

It is headed by Australia-based Peter Black, and includes Welsh officials Arwyn Jones and Martyn David.

An extra sheep shorn by Weeds was rejected by the judges, but convenor Peter Black, said the quality ratings have been comfortably within the requirements.

The shearers had a one-hour break before heading into the third run from 11.30am to 1.30pm, and the countdown run from 2pm to the end at 4pm.