Fire crews remain at the scene of a large vegetation fire beside the Kaiapoi motorway this morning, almost 12 hours after the blaze began.

The fire broke out shortly before 9pm on Tuesday in a 30m by 30m patch of vegetation near the State Highway 1 off-ramp and the intersection with State Highway 71, on the northern edge of Kaiapoi.

Fire and Emergency New Zealand spokesperson Bailey Wells said crews from Kaiapoi, Sefton and Pines Beach were at the scene on Wednesday morning.

A digger was being used to pull apart and turn over the slash pile so firefighters could extinguish any remaining hot spots.

Wells said the fire was under control, although flames or smoke could remain visible from the road and crews were expected to be at the site for much of the day.

Firefighters monitored the blaze overnight before returning with heavy machinery on Wednesday morning.

NZ Transport Agency warned motorists to take care while travelling through the area.

The cause of the fire was not yet known.