Authorities ordered an investigation after at least 11 poor and elderly people went blind following cataract surgeries performed at a free medical camp run by a charity in northern India.

The operations were performed on November 4 on dozens of patients over 50 years old from both Amritsar and nearby Gurdaspur, in Punjab state, said Ravi Bhagat, a top official in Amritsar city.

Some of the patients reported this week that they had lost their eyesight or were suffering infections, Mr Bhagat said.

Doctors in Amritsar are treating some of the patients. Police have launched an investigation, and detained at least one doctor in Gurdaspur.

Every year, thousands of people, especially in rural areas without proper health facilities, undergo cataract operations in medical camps held by health authorities and welfare groups.

The case once again highlighted the perilous state of health care in India, where hundreds of millions of poor people without access to doctors or health insurance are forced to seek treatment at medical camps because of poor services and corruption at government hospitals.

Last month, 13 women died after allegedly taking tainted drugs after undergoing simple sterilization surgeries in the central state of Chhattisgarh.