“Countries need to develop their own laws around this quickly, or improve their access to surrogacy for their own citizens, so they don’t have to go offshore to do this,” he added, referring to major sending countries like China, where surrogacy is illegal, and the United States.

After Cambodia announced a ban on commercial surrogacy in 2016 while legislation was being considered, an Australian nurse and two Cambodian assistants were convicted of running an illegal commercial surrogacy clinic there. They were later sentenced to one and a half years in prison.

But Mr. Everingham said Chinese agencies had been taking clients offshore for surrogacy over the past six or seven years, partly because of high rates of infertility in China and the recent relaxation of that country’s one-child policy, which has made many couples newly eligible to have a second child. He said that the Chinese agencies had long been willing to operate under the radar in Cambodia.

And despite the 2016 ban, he added, surrogates are also still being flown into Cambodia from other countries, including the United States, for in vitro fertilization because it brings down the overall cost of surrogacy for prospective parents to about $110,000 from $135,000. He said the procedures were typically carried out in Cambodia by visiting foreign doctors who rent facilities.

Keo Thea, the Phnom Penh anti-trafficking police chief, was quoted by Reuters as saying that the surrogacy operation had already provided about 20 babies to clients in China. He said the five people who were arrested, including a Chinese manager, were charged with both human trafficking and “being intermediaries in surrogacy.”