A pedestrian died on Wednesday after being struck in the head by what's thought to be a metal pole that plunged from a demolition site in Mong Kok.

Police say a man was arrested in relation to the incident, which happened at about 2pm outside Cheong Fat Mansion in Cheung Wong Road.

The victim, who is in her sixties, was rushed to Kwong Wah Hospital where she was declared dead.

The pole involved is said to be about 70cm in length.