Eight Indian women have died and 20 others are in a critical condition after having sterilisation surgery under a free government-run programme to help slow population growth.

A total of 83 women, all poor villagers under the age of 32, had the operations on Saturday in a hospital outside Bilaspur city in the central state of Chhattisgarh.

All 83 surgeries were conducted within six hours, said the state's chief medical officer, Dr SK Mandal.

"That is not usual," he said, but declined to comment further on what might have gone wrong until post-mortem examinations are conducted on the women.

Each of them had received a payment of 600 rupees (£6) to participate in the scheme, Dr Mandal said.

The women were sent home on Saturday evening but more than two dozen were later rushed in ambulances to private hospitals after becoming ill.

By today, eight had died - apparently from either blood poisoning or haemorrhagic shock, which occurs when a person has lost too much blood, state deputy health director Amar Singh told the Press Trust of India news agency.

Twenty other women were in critical care, according to the district magistrate, Siddharth Komal Pardeshi.

"Their condition is very serious. Blood pressure is low," said Dr Ramesh Murty at CIMS hospital, one of the facilities where the sick women were taken. "We are now concentrating on treating them, not on what caused this."

The state suspended four government doctors, including the surgeon who performed the operations and the district's chief medical officer. It also will give compensation payments of about £4,000 to each of the victims' families.

Chhattisgarh chief minister Raman Singh said "it appears the incident occurred due to negligence" by doctors.

Prime Minister Narendra Modi said he had spoken to Mr Singh and urged a thorough investigation.

The state's surgeons have met to discuss whether to continue with scheduled operations, with a target of 180,000 for the year ending in March set by the central government, Dr Mandal said. He said the quota for Bilaspur district for the year was around 12,000.

A spokeswoman for the Health Ministry declined to confirm whether the central government was setting sterilisation quotas. India's central government had said it stopped setting targets for sterilising women in the 1990s.

Activists blame the quotas for leading health authorities to pressure patients into surgery rather than advising them on other forms of contraception.

"These women have become victims because of the target-based approach to population control," said Brinda Karat of the All India Democratic Women's Association. She demanded that the state's health minister resign.

India's government - long concerned about rapid growth in a country whose population has reached 1.3 billion - offers free sterilisations to both women and men who want to avoid the risk and cost of having a baby, though the vast majority of patients are women.

In many cases, they are offered a one-time payment for undergoing surgery amounting to about a week's pay for a poor person in India. Hundreds of millions of Indians live in poverty.

India has one of the world's highest rates of sterilisation among women, with about 37% undergoing such operations compared to 29% in China, according to 2006 statistics reported by the United Nations. During 2011-12, the government said 4.6 million Indian women were sterilised.