A woman has been hit and killed by a bus while crossing the road at pedestrian lights in Melbourne's north-west.

It is believed the woman was walking her dog and crossed at the lights on Mickleham Road, Tullamarine, near the entry ramp to the Tullamarine Freeway.

The woman, who is yet to be formally identified, was hit just after 5.30am on Thursday and died at the scene.

Police at the Mickleham Road pedestrian lights near the entry ramp to the Tullamarine Freeway where a woman was believed to have been crossing when she was struck and killed. Credit:Scott McNaughton

The bus was travelling south on Mickelham road at the time.