UPDATED 6.19PM: Canterbury police are calling on a tractor driver and two cyclists to come forward in relation to the massive scrub fire burning near Arthur's Pass.

The blaze has incinerated over 330 hectares of wilding pines and grasslands on Flock Hill Station.

Detective Inspector Greg Murton says the fire appears to have started in four locations along the highway yesterday.

He says footage shows two cyclists and a tractor driver close to where the fire is believed to have started - and want to speak to each of them as key witnesses.

Fire crews still battling the fire have got it largely under control thanks to more favourable weather.

DOC fire technical support Craig Alexander says they moved into a second phase today, and hope to have it fully under control by tonight

"We've got at least twenty-five firefighters coming in to deployed out on the ground first thing in the morning," he says.