Sydney: Police are investigating a fire that extensively damaged an adult bookshop in St Marys last night.

Police and fire services were called the shop on Station Street at around 8pm following reports of a fire.

The building was well alight when they arrived, with smoke and flames coming from the second floor.

Firefighters managed to contain the blaze, however, the building sustained extensive damage. No one was injured during the fire.

The cause of the fire is unknown. A crime scene was set up and will be examined by fire investigation officers later today.