Police are still searching for three men who stole more than $1 million worth of second-hand watches in a Hong Kong smash and grab that took less than 20 seconds.

They hit a jewellery store on Yat San Street in Yuen Long, in the New Territories, about 9pm on Tuesday. A 34-year-old male staff member was inside the shop when one of the trio smashed its display window with a hammer. The other two men grabbed the valuables, mostly Rolex watches, police say. All three were wearing gloves, masks, hats and hoodies.

Security camera footage shows the hammer-wielding perpetrator guarding the store entrance while his accomplices load watches into their rucksacks.

A police spokesman says the man with the hammer threatened the employee.

The three robbers fled on foot before officers arrived.

It was the city’s fourth smash-and-grab case since March last year.

In December, three masked men used a sledgehammer to break into a pop-up store for online luxury bazaar Guiltless in Central and fled with 15 designer handbags worth $1.44 million.

In September, three thieves fled on a motorbike with $24 million worth of jewellery after smashing a store window with hammers at the Tsim Sha Tsui branch of Chow Sang Sang Jewellery store on Canton Road.

Six months earlier, in March, a masked robber took just seven seconds to smash a display window with a hammer and make off with a diamond ring worth $5.26 million from the Tsim Sha Tsui branch of 3D-Gold on Nathan Road.