NEW DELHI - Police in India are raiding hospitals and guest houses in a widespread investigation into the illegal sale of organs for transplant.

Officials say kidneys were removed from up to 500 poor labourers and sold to wealthy patients.

It is unclear if the poor people actually sold the organs or whether they were duped by dozens of doctors allegedly involved in the scheme.

Officials say that, either way, it is illegal to sell human organs for transplant in India.

The scam, centred in Gurgaon -- a posh suburb of New Delhi -- used luxury cars outfitted with blood-testing machines to test donors on the fly as well as sophisticated surgical equipment hidden inside a residential neighbourhood.

A waiting list seized by authorities contained the names of some 40 people from at least five countries.

The investigation is ongoing and police continued to raid hospital offices and guest houses, Gurgaon Police Commissioner Mohinder Lal told reporters in Gurgaon on Monday.

The primary suspects, who police said have been tied to organ transplant rackets in the past, were believed to have fled the country, Lal said.

"We suspect around 400 or 500 kidney transplants were done by these doctors over the last nine years,'' Lal told reporters.

There long have been reports of poor Indians illegally selling their kidneys, but the transplant racket in Gurgaon, broken up following a tip from a victim, is one of the most extensive to come to light.

Mohd Salim, a man who lost his kidney, said that in his case, a stranger approached him to offer work.

"I was taken to a room with gunmen,'' Salim told the NDTV television news channel. "They tested my blood, gave me an injection, and I lost consciousness. When I woke up, I had pain in my lower abdomen and I was told that my kidney had been removed.''

He didn't say if he was paid, but the Hindustan Times newspaper reported that those who were paid for their organs earned the equivalent of between C$1,250 and C$2,500.

The kidney ring had a waiting list of dozens of people from India, the United States and Greece, according to the Hindustan Times.

Several foreign patients waiting for transplants were at the facilities when police raided them Friday, but they were allowed to return to their home countries without being held for questioning.

The case has sparked outraged headlines -- and ignited a national discussion of organ transplant law, with the Indian Medical Association on Monday calling for legislation to make organ transplants easier.