CCTV footage reveals how suits pulled off record Graff Diamonds heist

This was a well-planned robbery with a number of vehicles used to help the robbers escape.

Detective chief inspector Pam Mace

A massive police hunt is underway in Britain for two men believed to have pulled off the nation's biggest ever jewellery heist.

The armed robbers, dressed in smart suits and ties, made off with an estimated £40 million ($A78.65 million) in gems from the exclusive Graff Diamonds store in central London during their daring daylight robbery.

Warning shots were fired and a female staff member briefly held hostage during the holdup, which lasted just minutes.

The men, who both carried handguns, stole 43 items from the store on New Bond Street, in the heart of London's fashionable Mayfair district.

Their haul included a white and yellow diamond daisy necklace, double hoop diamond earrings, a platinum white Marquise diamond ring and a men's chronograph 45mm watch.

Police believe the robbery is the biggest ever jewel heist ever seen in Britain, ironically topping a £23 million ($A45.23 million) raid at the same store in 2003 and a £30 million ($A58.99 million) raid on Cartier in 1997.

While the robbery occurred last Thursday, police only revealed the extent of the heist on Tuesday as they launched an appeal for witnesses to come forward.

The men walked into the well-guarded Graff Diamonds - whose celebrity clients include supermodel Naomi Campbell and Victoria and David Beckham - about 4.40pm on August 6 and threatened staff with handguns.

In just a matter of minutes they ordered staff to hand over a variety of necklaces, bracelets, rings and watches before fleeing, seizing a female staff member on their way out.

The woman was left on the street as the robbers fired a warning shot into the air and leapt into a waiting blue BMW to make their escape.

Police said the BMW weaved its way through nearby streets before colliding with a black taxi.

The men abandoned their vehicle, firing another warning shot into the ground, and switched to a silver Mercedes which drove them a short distance to another waiting getaway car.

Police believe at some point while the men switched cars, they handed the jewels over to a waiting motorcyclist who sped off with the valuable haul.

Releasing CCTV images of the men on Thursday, Metropolitan Police Flying Squad detective chief inspector Pam Mace appealed for the public to find the robbers.

"This was a well-planned robbery with a number of vehicles used to help the robbers escape," she said.

"These men are extremely dangerous and fired at least two shots in busy London streets as they made their getaway.

"Someone knows who these men are, they would undoubtedly have spoken about it beforehand or boasted about it afterwards.

"I would urge anyone who recognises them, knows the whereabouts of the jewellery or has any other information to contact us."

Both men, believed to be in their 30s and about 182cm tall, wore grey suits and white shirts with ties.

One was of Caucasian appearance with a slim build, dark hair and stubble.

The second man was black with a short Afro hair style