Sydney CBD jewel heist in broad daylight

Two thieves have staged a jewel heist in broad daylight in Sydney's CBD before speeding off in a Porsche.

Armed with what is believed to be a hammer, one man threatened staff at a jewellery store on the corner of King and Pitt streets before making off with cash, jewels and watches about 4.45pm on Thursday, police said.

He then fled to a waiting blue Porsche Coupe get-away car, which crashed into another vehicle as it sped through Surry Hills.

Police released CCTV footage on Friday showing the thief running into the store wearing a yellow hi-vis vest over a grey hoody, holding what appears to be a hammer and a bag.

The thief and the get-away driver both have their faces covered.

Police are appealing for witnesses, particularly those who might have filmed the robbery, to come forward.