A balcony has collapsed on Sydney's north shore, injuring eight people.

Police say they were called to the accident at the apartment building at Lane Cove just after 10pm (AEDT).

They say 11 people were on the balcony at the time of the collapse and that they all fell around seven metres.

Eight people were taken to hospital with a range of injuries, five thought to be serious but not life-threatening.

Fire and Rescue crews say it was lucky no-one was buried in the rubble.

Engineers will return to the site on Thursday morning to try to determine what caused the balcony to give way.