Two men were killed when their B-double truck veered off the Hume Highway and crashed 100 metres down an embankment on Tuesday.

The truck carrying magazines was travelling near Gunning, about 70 kilometres north of Canberra, just after midnight. It crossed the median strip into the northbound lanes of the highway and crashed through a guard rail, police said, adding the reason for the accident was not yet known.

The driver of the truck, a 59-year-old from Western Australia, and his passenger, a 58-year-old from NSW, died at the scene.

The deaths took the NSW road toll to 347 killed in 319 fatal crashes.

The ACT's road toll currently stands at 11, almost twice as high as the record low achieved last year.

Anyone with information about the crash should call Crime Stoppers on 1800 333 000.