This is the eerie moment thousands of crows circled above a hospital in Inner Mongolia.

The flock was seen gathering in the skies above Chifeng City Hospital on the evening of October 26.

Footage captured by Ms Wang shows the birds flying above the building, with some perched on the rooftop.

Local reports said that this phenomenon is not a first for the area.

Officials from the Hongshan District Forestry and Grassland Department attribute the behaviour to the 'urban heat island effect,' which causes the city to remain warmer at night, attracting the crows.

Bird experts caution that crow droppings are highly corrosive and can damage vehicles and clothing if not cleaned promptly.

Crows may gather for various reasons, including mating season, communal roosting at night for protection from predators, ritualised behaviours such as gathering around a deceased fellow to display specific actions or mobbing predators to drive them away from their territory.