A woman catching a bus into Sydney's CBD had a chunk of her hair cut off by passengers who were sitting behind her, witnesses say.

The incident occurred on the route 339 bus, which travels from Clovelly into the city, about 9.40am on Wednesday and left the woman distraught and in tears.

The incident occurred on a route 339 bus from Clovelly to the city. Credit:Lisa Wiltse

A male passenger sitting next to the woman - who he estimated was in her early 20s with long, dark hair - told Fairfax Media that a "creepy, freaky" man and woman had been sitting in the seat behind them.

"The girl turned around and asked the man 'did you cut my hair?' " said the passenger, who did not wish to be identified.