Police have launched a massive manhunt for up to six men who they say escaped with a HK$28 million ($3.6 million) ransom in one of the biggest kidnapping cases in Hong Kong in recent years.

The men are said to have seized the daughter of a billionaire at her luxury home at Clear Water Bay after a break-in and robbery on Saturday.

Police said the kidnappers are from the mainland. Two are aged between 26 and 29 and were wearing dark jackets, bluejeans and sports shoes. One has a scar on his right palm. Another two are 1.6 meters tall and wore white coats.

According to reports, five or six masked men broke into the billionaire's detached house and ransacked the premises. They took away HK$2 million in cash and valuables, as well as the owner's 29-year-old daughter, who was alone in the house. The family reported the kidnapping to the police, and the case was passed to the Kowloon East Regional Crime Unit.

The billionaire, who is said to be in the real estate business, received a call from the kidnappers, demanding a ransom of HK$50 million in exchange for his daughter, say police. The demand was later lowered to HK$28 million after negotiations.

The abductors called the billionaire again on Tuesday night to make arrangements to pick up the ransom, the reports say. The money was placed in 28 bags, each containing HK$1 million. The kidnappers escaped in a white car after receiving the money, and officers found the woman unhurt in the Tseung Kwan O district.

A citywide manhunt was then launched, with roadblocks being placed on all main routes out of the city. The areas affected included Wong Tai Sin, the Cross-Harbour Tunnel, Yuen Long and Tseung Kwan O.

Heavily armed police wearing helmets and bulletproof jackets stopped suspicious vehicles, and large numbers of officers searched the areas around the woman's home in Kowloon Peak, also known as Fei Ngor Shan, with the assistance of helicopters.

Retired detective Lam Kin-keung described the crime as "well-organized" as the suspects, who are not local, were able to escape in an unfamiliar city.

"It is possible that the kidnapping was an improvised crime," he said. "It is likely that burglars came to realize that the owner of the house was rich after ransacking it."

stushadow@chinadailyhk.com