Thieves attacked two shop workers before stealing Asian jewellery worth hundreds of thousands of pounds, Scotland Yard said.
Detectives are hunting two men who ransacked more than 500 items worth about £600,000 from the Aron Jewellers, in High Street North, East Ham, east London.
The suspects tied up and gagged a woman and elderly man who work at the store as they spent almost half an hour emptying display cabinets of bracelets, necklaces, bangles and rings, the Metropolitan Police said.
Aron Jewellers specialises in Asian jewellery and many items are purchased by clients specifically for Asian weddings, police said.
The two men visited the shop at about 11.30am on Tuesday May 29 and were allowed access through a security door by the female staff member.
She recognised the men who had visited the shop on three occasions the previous day and left a £20 deposit on a gold chain, police said.
The suspects asked to view another item of jewellery in a display cabinet before one of the men jumped over the display counter.
He grabbed the woman around the neck and put something over her face, causing her to pass out, police said.
Hearing her scream, the elderly male staff member ran to the front of the store and was confronted by the other suspect. He was thrown to the floor, before something was stuffed in his mouth and he was held face down, police said.
Both victims then had their hands and feet tied up and the woman had duct tape put over her mouth.
The suspects are described as men, both Asian, possibly from Pakistan and aged between 30 and 40. One was wearing a yellow top with a black and white stripe at the bottom. The other was wearing a black hooded top.
It is believed the men could have been in the area for about half an hour waiting for the staff to replenish the displays with jewellery, which is kept in a secure place overnight.
The Met said every item of jewellery has the owner's certified hallmark and can be easily identified. The street is very busy, with many pedestrians and vehicles, police said.
Anyone with information should contact Flying Squad, North East Branch on 020 8345 4226 and ask for Dc John Conner or Dc Simon Cuthbertson.