PHNOM PENH (Reuters) - Thirty-three pregnant Cambodian women who were carrying babies on behalf of Chinese clients have been discovered during a raid on an illegal commercial surrogacy operation, police said on Saturday.

Five people, including a Chinese manager, were arrested following raids at two apartments in the Cambodian capital, Phnom Penh, police said.

Cambodia had been a popular international destination for infertile couples looking to have babies through commercial surrogacy even though it is was made illegal in 2016.

Keo Thea, director of Phnom Penh’s anti-trafficking office, told Reuters on Saturday that five people, including four Cambodian women and the male Chinese manager, had been detained during a police raid on Thursday.

“Our authorities have charged them with human trafficking and being intermediaries in surrogacy,” Keo Thea said.

The pregnant women would not face charges at the moment, he said.

“They are carrying babies for Chinese nationals,” he said, adding that each woman was promised $10,000 for the service.

Once a woman becomes pregnant she receives $500. When the baby is delivered the terms of her agreement are that she will be paid $300 a month until the full $10,000 is paid off, Keo Thea said.

Keo Thea said the surrogacy operation had already provided about 20 babies to clients in China.

“Some were born in China and some were born in Cambodia,” Keo Thea said.

Clinics based in Asia are increasingly eyeing China, where health officials estimate that 90 million couples have become eligible to have a second child after a decades-old one-child policy was relaxed in 2015.

There are no official estimates of the number of Chinese babies delivered by surrogates, but media say it exceeds 10,000 every year.

Thailand and India have blocked foreigners from using commercial surrogacy services following a series of cases that raised concern about exploitation.

Thailand banned the practice in 2015 and subsequently several Thai clinics move across the border into Cambodia until commercial surrogacy was banned there the following year.