The Indian government told thousands of striking airport workers on Friday that it would not reverse a decision to hand over New Delhi and Mumbai airports to private firms to modernize and manage.

Passengers battled through heaps of garbage at the two busy airports on the third day of the protest, in which nearly 23,000 workers fearing job losses have stayed away from work.

Prime Minister Manmohan Singh appealed for an end to the strike at a meeting with union leaders, who met later to discuss their response. Television reports said they would meet again on Saturday.

"There is no question of reversing the decision on Delhi and Mumbai," Civil Aviation Minister Praful Patel told reporters.

Thousands of passengers at New Delhi and Mumbai airports, the nation's biggest and those worst affected by the strike, kicked away discarded coffee cups and sweated heavily as air-conditioners packed up and cleaners did not report for work.

Friday was the third day of the walkout called by the Airports Authority Employees Union, which opposes the government decision to privatize the two airports.

But airline officials said the morning flights all took off on schedule.

The privatization plans are also opposed by communist parties, which give crucial support in parliament to the Congress-led coalition government but have backed the strike and say airport modernization should be carried out by the state.

The strike began on Wednesday after the government awarded contracts to two private consortia involving overseas companies to modernize and manage the New Delhi and Mumbai airports.

The decision to modernize the two shabby, run-down airports is seen as a sign of India's determination to accelerate its infrastructure development to keep pace with one of the world's fastest-growing economies.

The airports have congested waiting areas, a lack of comfortable seating, slow baggage handling and unreliable power supplies, making travel a misery for the fast-expanding middle class who increasingly make long-distance journeys by air.

On Friday, the New Delhi terminal was strewn with empty plastic bottles, cups and paper. About 200 workers shouting "Down with the government" and "Down with privatization" protested in front of the airport despite a court ruling that demonstrations should not affect the functioning of the hubs.

At the international airport in Kolkata, the air-conditioning stopped and passengers complained of a lack of drinking water, luggage trolleys and working conveyor belts.

The Airports Authority awarded the contract for Delhi Airport to a consortium led by India's GMR group and German airport operator Fraport, and that for Mumbai Airport to a group led by India's GVK Industries and the Airports Company of South Africa.