Traffic cameras showed a long queue of vehicles on the road.
A spokeswoman for the firm said: “A road traffic incident is currently blocking the A9 at Drumochter pass between Wade Bridge and Dalnacardoch Lodge.
“A car has collided with a BEAR spreader which was assisting an HGV in snow conditions.
“There are no reported injuries at present and Police Scotland are in attendance.”
To the east, another high-level road, the A93 between Glenshee and Braemar will remain shut until tomorrow, Traffic Scotland, the Scottish Government’s driver information service, said.
Met Office yellow - “be aware” - severe weather warnings for snow are in force for the whole of Scotland apart from Orkney until midday tomorrow.
A spokesman said: “A band of heavy rain will spread eastwards across northern Britain today. The rain will be preceded by snow for a time, and across higher level roads of Scotland it will remain as snow, mainly above 400m (1,300ft).
“At these levels, the snow combined with gales is expected to give some very poor travelling conditions, whilst at lower levels there is a risk of localised flooding.”
Forecasters warned that from 9pm tonight, snow would fall at lower levels: 2-5cm (0.8-2in) above 200m (670ft) and up to 10cm (4in) above 300m (1,000ft).
They said: “Clear spells will lead to a risk of icy stretches. The public should be aware of the likelihood of some difficult driving conditions and the possibility of travel disruption.”
The A9 at Drumochter is 1,500ft above sea level, while the A93 at Glenshee is 2,200ft.