Passers-by grab the cash fallen out of a armor van in Hong Kong on December 24, 2014. [Photo/Sina.com]

An armor cash carrier spilled HK$35 million ($4.51 million) on to a highway in Hong Kong on Wednesday, bringing traffic to a halt as people rushed to grab the money.

The van was carrying a total of 30 containers of cash from Hong Kong Island to Kowloon when the money in three boxes fell out on the Gloucester Road, police said.

The rear door of the vehicle was reportedly not properly closed but investigation is underway.

TV footage shows drivers and pedestrians scrambling to scoop up the money scattered all over the road before armed police officers rushed to seal off the area.

A witness told the South China Morning Post that he saw a lady walk off with 10 cash-bricks.

"I saw a lady with 10 of them, easily. She had an armful of bricks of cash - it was a much as she could carry," the witness was quoted as saying by the newspaper.

Authorities said HK$15.23 million ($1.96 million) of cash is missing and they will use the serial numbers to trace it back.

Police urged people who picked up the cash to return it as soon as possible, warning that otherwise they could face up to 10 years in jail for theft.