Hundreds of foreigners were arrested in a raid at an alleged Chinese sex hub with 'prostitution dens' and 'torture chambers' in the Philippines.

Police said 731 visitors from China, Vietnam and Filipino locals were detained for interrogations when authorities converged on the six-storey building rented by offshore gaming company Smart Web Technology in Pasay City, Manila, on October 27.

The inter-agency task force led by the Department of Justice (DOJ) executed a search warrant and conducted a sweep of the company, which was reportedly a front for sex and human trafficking.

Officers said they found in the premises several karaoke rooms where sexual acts were believed to have taken place.

Footage of the raid also showed a neon-lighted 'aquarium' - a showroom for patrons where alleged young prostitutes, all aged under 25 without any children, were lined up and displayed.

After taking their pick, the VIPs were said to have taken the women to bed in rooms just outside the 'aquarium'.

Photos taken by the Philippine Anti-Organised Crime Commission (PAOCC) also showed various implements such as bats, clubs, cuffs, sticks, and an airsoft gun allegedly used to torture erring employees.

Nine people suspected to be Smart Web executives have been arrested and will undergo inquest proceedings.

DOJ Undersecretary Nicolas Felix Ty told local media: 'In particular, the crime that was found is sex trafficking based on the intelligence report.

'As you can see, there's KTV, on other floors there are rooms for extra service. There's even a menu of different sexual services.'

At least nine Chinese workers have confirmed that torture and kidnapping had taken place at the suspected sex den, local media reported.

They were allegedly beaten with sticks, kicked, and punched for not meeting quotas set by their bosses. The staff said they were required to trick 10 people into falling for the company's 'love scam', and were made to work long hours.

The raid comes as Philippine lawmakers call for a crackdown on the offshore gaming companies, known as Philippine Offshore Gaming Operators (POGO) or internet gaming licensees (IGL).

The companies - most of which are Chinese - proliferated in the Philippines during former President Rodrigo Duterte's term as he pivoted toward warmer relations with China, where gambling is illegal.

However, IGLs had become a hotbed for crimes like prostitution, human trafficking, fraud, and kidnapping for ransom.