Port Stephens police Inspector Dan Skelly said reports of bicycle theft had risen across the district - in particular in Nelson Bay - since the start of the summer holiday period but had not slowed down.

"Nearly every day we have expensive bikes going missing," he said. "All the bikes that have been reported stolen have been preventable.

"A lot have been going missing from the holiday parks around the Bay area where they've been chained up with flimsy locking devices. Some have been left unsecured or not properly secured."

Last Tuesday two expensive bicycles were stolen in Nelson Bay. In the same week, an electric bike worth $7500 was stolen from outside a shop in Maitland, which also falls within the Port Stephens Hunter Police District.

Inspector Skelly said investigators were following up with a number of suspects but he added that theft was an opportunistic crime that is preventable by taking precautions.

"We appeal to the public about securing their bikes with decent locks and chains," he said. "Some of the bikes being stolen are worth over $10,000 but they're being locked up with something worth $100.

"Secure your bike with good quality chain and lock, preferably to an immovable solid object. The locking device you use to secure an expensive bicycle should be consummate with the value of the bike.

"Good quality locks and cut resistant chains are expensive like the bike you are trying to protect."