Hundreds of thousands of erectile dysfunction pills, anti-depressants and other psychotropic drugs have been seized in Hong Kong this month with four people arrested on suspicion of running a medication mail service without a permit, customs officers said on Sunday.

The 1.4 million pills, found in a remote village house in Mui Wo and at a subdivided factory unit in San Po Kong, are believed to be worth around HK$80 million in total.

Officers said the hauls mostly comprised of generic drugs from India.

It's believed the pills were being posted to dozens of places around the world.

A senior customs investigator, Hong Yan, said they were looking into whether the two cases are linked.

"We found that the two syndicates operate in a very similar fashion. They both rented a unit as a centre for packaging and storing the medicines," he told a press conference.

"They also hired foreigners to package and post the medicines overseas. Furthermore, inside the units, the ways the drugs were categorised and stored were very similar."

Officers said two women arrested in Mui Wo at the start of the month had since been released on bail, while two women arrested in San Po Kong were still in detention.