Philippine police on Thursday rounded up 357 foreigners accused of duping Taiwanese and Chinese citizens in an online scam.

The mostly Chinese and Taiwanese suspects were arrested in simultaneous raids on 20 houses in metropolitan Manila and nearby Antipolo city, said Philippine National Police investigation group chief Samuel Pagdilao.

Those arrested were members of a syndicate that pretended to represent police, prosecutors, courts and insurance companies and told the victims that their bank accounts were being used for money laundering and terrorist financing, he said.

He said the victims were pressured to transfer their money to a "safe account" provided by the syndicate.

The syndicate raked in at least 20 million pesos ($472,000) each day using the scam, he said.

Presidential Anti-Organized Crime Commission head Paquito Ochoa said the arrests were the largest single-day operation against organized crime in the country.

Pagdilao said Chinese police requested assistance in pursuing the syndicate after they determined that an Internet address used by the scammers originated in the Philippines.

The suspects are being held in a gymnasium inside a police camp in Laguna province's Canlubang township south of Manila.