A passenger was stuck on a Citybus after failing to unfasten the seatbelt to alight, with bus operator saying a piece of aluminium foil found inside the buckle was to blame.

The man, 40, was trying to get off a 795X Citybus bound for So Uk near Sham Shui Po Sports Ground on Thursday morning.

He was unable to unbuckle his seatbelt, prompting 16 firefighters and four paramedics to be dispatched.

While waiting to be freed, the man reportedly felt unwell and was later sent to Caritas Medical Centre.

Citybus said the driver stopped the bus at Cheung Wah Street and reported the incident after being notified of a passenger failing to unbuckle.

The firm said an inspection found a piece of aluminium foil stuffed inside the buckle, suspecting someone was deliberately trying to damage the seatbelt.

The Transport Department said it's highly concerned about the incident and told Citybus to submit a report and take follow-up action.

The department urged franchised bus operators to conduct routine checks to ensure all seatbelts work properly.

It added the government has been closely monitoring the implementation of the mandatory seatbelt law for buses and minibuses that took effect on Sunday, and vowed to listen to the views of passengers on the matter.