A truck driver desperately tried to alert another truckie that a hitch-hiker was hanging on to the back of his B-double on a highway in the dark.

But the hitcher - a man believed to be around 30 - died after falling off the truck on the Sturt Highway - about seven kilometres east of Collingullie - about 10.45pm yesterday, police say.

Police believe the man climbed onto the truck when it stopped at traffic lights in Wagga Wagga.

Do you know more? Message 0424 SMS SMH (+61 424 767 764) or email us with information.

When another driver spotted the hitch-hiker clinging on, he tried calling the B-double driver over UHF radio, then flashed his headlights.