Police and Roads and Maritime Services crews have been on scene since the early hours of this morning to divert traffic after snow fell in the area last night.

An RMS spokesperson said people who need to travel between Armidale and Glen Innes will be diverted along Thunderbolts Way and the Gwydir Highway via Inverell.

Armidale Police Station supervisor Sergeant Chris Pieterse said trucks were unable to pass through the area this morning and the highway wouldn't be reopened until the ice had thawed.

He said there were reports as many as two trucks had jack-knifed on the highway after losing traction on the slippery road, but the details of the incidents weren't made available.

"It snowed last night and got colder and about two inches of it turned into ice," Sergeant Pieterse said.

"It made the road impassable and subsequently the RTA has made detours except for the trucks which will be stopped for a while."

Sergeant Pieterse urged motorists to "be mindful" of black ice on local roads and to travel with caution.