Robbers smashed their way into a pawnbrokers using a hammer and made off with jewellery.
Four suspects fled on motorcycles after two broke in to a window display at H&T Pawnbrokers, in Station Road, Hayes.
Police were called to the shop shortly before 1.30pm on Monday (March 16), but have made no arrests. The Metropolitan Police's Flying Squad is investigating.
H&T Pawnbrokers said two members of staff were inside the store when the break-in happened, but no one was hurt.
A spokeswoman added: "The two robbers managed to get access to the retail stock in the window. A small amount of this was taken.
"They did not gain entry to the back of the store, where customer property is kept.
"All customer property is therefore safe and locked away under high security."
Jas Obhrai, who owns World Wines, also on Station Road, said he arrived at the scene shortly after the robbery.
He said: “Everyone was just crowding around as soon as the police turned up.
"It's not something we see too often around here. People couldn't believe what had happened.”
He added: “This is becoming quite regular now in and around London – jewellery shop smash-and-grabs. Liverpool Street, I get it. You wouldn't expect it in Hayes town though.”
Anyone with information should call 101. Alternatively, call Crimestoppers anonymously on 0800 555 111.