Philippine authorities have seized more than 160 kilograms (350 pounds) of methamphetamine concealed in tea wrappers in their second-largest drug haul this year in a sign of how the problem has persisted despite the president's bloody crackdown on illegal drugs.

Philippine Drug Enforcement Agency chief Aaron Aquino says three Chinese nationals and a Chinese-Filipino man, who works as an interpreter, were arrested late Tuesday during "buy-bust" raids in an upscale residential enclave and outside a shopping mall in metropolitan Manila.

Aquino said Wednesday the drugs were concealed in tea wrappers similar to those seized in Malaysia, Thailand and Myanmar and indicated an international syndicate was behind the trafficking.

Thousands of mostly poor drug suspects have died in President Rodrigo Duterte's crackdown on illegal drugs since he took office in mid-2016.