A unique pink Argyle and white diamond ring valued at $577,000 has been stolen from an auction centre in central Sydney.

New South Wales Police said an employee discovered the ring was taken from a display counter at the centre in Ralph Street in Alexandria on Saturday, between 12.30pm and 1.25pm.

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About 100 people were inside the centre around the time the ring was stolen, police said.

Each of the diamonds in the ring is laser-inscribed with a serial number.

Pink Argyle diamonds are rare gems sourced from the Argyle Diamond Mine in the East Kimberly region, which produces 90 per cent of the world’s pink diamonds.

A 2.51-carat fancy deep pink gem from the mine attracted a record price for an Argyle diamond of more than $2 million in October 2013.

Police have encouraged anyone with information on the theft to contact Crime Stoppers.