A white Toyota four-wheel drive and a white Dodge SUV collided on the Barton Highway at Wallaroo, about 3.5 kilometres north of the ACT border, about 8am on Friday.

Inspector Alison Brennan said police believed both cars were carrying four people, including a number of children aged between eight and 12.

Both of the people killed were passengers in the same car, but Inspector Brennan would not say which one.

The drivers were among the six taken to hospital, where they will undergo mandatory testing.

One of the cars also crashed into a bronze Mazda in a secondary collision, but none of that vehicle's occupants, including a toddler, were injured.

Inspector Brennan said police would not release the ages and genders of the people killed until their families had been notified.

The road was likely to remain closed in both directions well into Friday afternoon, but Inspector Brennan hoped it would reopen before nightfall.

Diversions were in place, but traffic was backed up for several kilometres in both directions.

Specialist crash investigators were at the scene on Friday morning, and had deployed a drone to take aerial photos of the wreckage as part of their investigation.

Inspector Brennan said though it was not yet clear what had caused the crash, it should be a reminder to all drivers.

"I can't tell you whether speed was a factor in this particular instance, but it's always good to remember that these things can happen so quickly," she said.

"Even if the signposted speed limit says 100 kilometres an hour, it may not be safe to drive at that speed.

"People need to drive to the conditions and be vigilant of what's around them."

Inspector Brennan urged anyone with information on the crash to contact Yass Police Station on 6226 9399, or Crime Stoppers on 1800 333 000, or via the website.