Police said they were raiding hospitals and guest houses Monday as part of their investigation into an illegal transplant racket that allegedly removed kidneys from up to 500 poor laborers and sold their organs to wealthy clients.

Police suspect that dozens of doctors were involved in the kidney racket, which had a waiting list of some 40 people hailing from at least five countries.

The scam, centered 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 neighborhood.

The sprawling investigation is ongoing and police are raiding hospitals' 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, have apparently 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 last week.

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

Accounts varied on whether the laborers were aware they were selling their kidneys or whether doctors removed them without their consent. Under Indian law, the sale of human organs is illegal under any circumstances, though organ donations are allowed.

Mohd Salim, a man who lost his kidney, said the scam began when a stranger approached him to offer him 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 $1,250.

The kidney ring had a waiting list of dozens of people from India, the United States and Greece, according to the Hindustan Times. Several patients waiting for a transplant were at the facilities when police raided them Friday, but they were allowed to return to their countries without being held for questioning.