NEW DELHI (AP) _ A doctors' strike that began in the capital to protest an affirmative action program at medical colleges spread Sunday, threatening to cripple services at major government health care facilities.

Medical students demonstrated across the country, angered by police violence Saturday against doctors protesting at government hospitals in the capital, New Delhi, and Bombay.

The protests were sparked by the government's decision to increase the percentage of low-caste Indians at state-run medical colleges to 49.5 percent of the student body. Currently, 22.5 percent of admissions entries are set aside for low-caste Hindus and students from ethnic minority backgrounds.

Similar affirmative action programs already exist in other state-run educational institutions, aimed at creating equal opportunities for low-caste Hindus, who have faced discrimination for centuries.

Emergency health services at New Delhi hospitals were the worst hit by the strike. Television stations showed dozens of patients on stretchers lying unattended outside emergency rooms, many of them poor people unable to afford private hospitals.

Students at seven medical colleges in western Gujarat state began a hunger strike. Medical students in the eastern state of Orissa and the northern Punjab state burned effigies of Human Resource Minister Arjun Singh during protests on Saturday and Sunday.

In Bangalore, the capital of southern Karnataka state, students at several technical education institutes joined medical students at a protest outside the local governor's house.

The Indian Medical Association, the main grouping of doctors in India, said it was preparing a plan for a nationwide action. Its executive body has called a meeting for May 20, said Sanjiv Malik, president of the association's New Delhi chapter.

Vinod Patra, the president of the Resident Doctors' Association at New Delhi's prestigious All India Institute of Medical Sciences, said the strike would continue until the government reverses its decision. Patra said the protesters also want an immediate meeting with Prime Minister Manmohan Singh.

Police on Saturday used batons and water cannons against doctors striking at the All India Institute of Medical Sciences and another hospital in the capital. Similar clashes occurred at state-run facilities in Bombay.

The government showed no sign of budging.

Commerce and Industry Minister Kamal Nath said the government was committed ``to affirmative action because we have to ensure growth that is inclusive.''

Despite laws against discrimination, India's lower castes _ 80 percent of India's 1 billion people by government estimate _ are still at the bottom in most social indicators, such as education, income, employment, asset ownership and debt.