Police in east China's Shandong province announced Wednesday that they have cracked two illegal organ-transplant clinics, arresting 18 people involved.

The clinics in the Huaiyin district of Jinan, capital of Shandong, were raided Sunday night as doctors were preparing for a kidney transplant, said an official with the city's police bureau.

Police were tipped off earlier this month, and then launched a probe with the city's health bureau against the two clinics. They found that vehicles and people regularly shuttled between the two clinics, which were not far away from each other, the official said.

They decided to raid the two clinics after 10 days of investigation.

China bans organ transplants from living donors except for spouses, blood relatives and adopted family members. However, reports about illegal transplants indicate there appears to be a large underground network profiting from the country's demand for donor organs.

Earlier this month, three doctors were arrested for illegally harvesting human organs in Hebei province. All three were licensed doctors from Shandong.

Jinan has launched an inspection of the city's medical institutions to crack down upon illegal organ transplants.