A police officer who was brutally attacked with a machete on Saturday morning has been overwhelmed by messages of support from workmates and the public, police say.

Tributes have poured in for senior constable Bruce Mellor, who was last night in emergency surgery to rebuild his face.

The army is investigating how a box of ammunition fell off the back of one of its trucks and was run over by a car.

A cold southerly is set to dump more snow on the Desert Road and bring a chill to much of the country.