Eight men who kidnapped a Hong Kong fashion heiress and held her in a cave as they negotiated a multimillion dollar ransom were sentenced to up to 15 years in prison on Friday, a Chinese mainland court said.

Queenie Rosita Law, granddaughter of the late textiles tycoon Law Tingpong, who founded the Bossini clothing chain, was abducted from her house in Hong Kong in April last year.

The 29-year-old was held in a mountain cave for four days before family members paid a ransom of HK$28 million ($3.61 million) for her release. Most of the gang fled to the mainland afterward, where they were captured.

Six of the defendants were found guilty of abduction and two others of disguising or concealing illegally obtained gains, a Shenzhen Intermediate People's Court spokesman said.

The ringleader, You Dunkui, was sentenced to 15 years for kidnapping, with the others being given terms ranging from 13 years to just under two, he said.

Another gang member, Zheng Xingwang, was sentenced to 12 years by a Hong Kong court last month after having confessed to a charge of forcibly taking or detaining a person for ransom.

Law and her boyfriend were asleep at her house in the quiet coastal Clearwater Bay area when six mainland Chinese men raided the house, tied them up and taped over their mouths, according to testimony at Zheng's trial.

They stole jewelry and cash worth about HK$3 million from two safes, after forcing Law to give them the combinations.

Law was tied to one of the gang members, who carried her on foot to a hillside cave 90 minutes' walk away. Her boyfriend was told to notify her father of the ransom demand.

Hong Kong police launched a massive search for the kidnappers, deploying hundreds of heavily armed officers, helicopters and marine vessels, and setting up roadblocks.

Almost all of the money has been recovered, including some buried on hillsides near the cave.

Although Hong Kong has low crime rates, it has seen some high-profile kidnappings, including the abduction in 1996 of one of city tycoon Li Ka-shing's sons, who was released after his father reportedly paid a HK$1 billion ransom.