The four criminals were filmed as the they calmly left the upmarket store on Thursday morning after filling up their bag with designer goods.
“That’s a hold-up,” said an astonished witness, as he filmed the drama on his mobile phone, before posting it on social media.
The robbers wore helmets with the visors down as they raided Chanel on the world-famous Place Vendome.
The square not only contains landmarks such as the Paris Ritz Hotel, but also the Ministry of Justice.
“There did not seem to be any security in the store all,” said another witness. “Everything happened in less than three minutes.
“The men pulled up on two bikes, and walked in. They got everyone in the store to lie on the floor, and then loaded up on jewellery and luxury watches.
“Then they left on their bikes with one of the gang showing off his assault rifle in open view.”
Nobody is believed to have been hurt in the robbery, before the criminals raced down Rue de la Paix, which leads just off Vendome.
Last September, Paris police caught three suspected armed robbers after opening fire on their car as they made their getaway from a £9million heist at a Bulgari store in Place Vendome.
The men, wearing suits and armed with guns, robbed the boutique before trying to get away in a car, and on scooters.
Police fired shots at the car near the Les Halles shopping centre, about 1.5miles away, leading to the arrest of the raiders.
Jewellery stores in Paris have been hit frequently by robbers over the years, and celebrity homes are also targeted.
In July, thieves made off with goods worth almost £2m from a Chaumet store near the Champs-Elysees, and a Dinh Van store was also hit in the same month.
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In October 2016, more than £7m worth of jewellery was stolen after American reality TV star Kim Kardashian was robbed at gunpoint by a group of masked men in her Paris hotel room.
