A woman is fighting for her life after being hit by a truck while walking her dog in central Auckland this morning.

The woman, aged in her 40s, was walking her dog on Greys Ave at 8.46am when she was hit by the truck, which is believed to have been reversing, police said.

She suffered serious leg injuries and was rushed to hospital in a critical condition.

The truck driver stopped at the scene and the truck has been towed for examination, police said.

A witness said there were still several police and fire staff at the nearby carpark of The Civic theatre on Mayoral Drive at around 11.30am.

"I wasn't here when it happened bu there's been lots of cops around. The road was blocked off for awhile and the truck had to be towed away."

The Auckland City Police serious crash unit is investigating.

Police said they are making ongoing efforts to contact the woman's next of kin.