Gunmen have raided the exclusive Louis Vuitton boutique in central Sydney.

Police say two men armed with a gun and a sledgehammer burst into the store on the corner of Castlereagh and King Streets just after midnight threatening workers and security guards.

Staff had been changing the store's window displays when they were forced onto the floor.

Officers have taken forensic evidence from the shop.

They're appealing for anyone with information or any witness to come forward.

Detectives also want to hear from people who suspect they're being offered genuine designer items at discounted prices.

The thieves escaped with tens of thousands of dollars worth of designer bags.