Reliance, India's largest private company, and ASA Mexico offered the government 46 percent of revenue it expected to earn after modernising and upgrading the airport, the Press Trust of India (PTI) news agency said.

Construction firm GMR Industries, based in the southern Indian city of Hyderabad, teamed up with the Frankfurt airport operator Fraport, finished second with a bid of 43.64 percent of revenue, the report said.

Others in the race were India's D.S. Construction along with Munich airport, Australian financial group Macquarie with partner Airport de Paris and India's GVK group which has tied up with the South African Airport authority.

The opening of bids for the modernisation of the Delhi and Mumbai airports came in the midst of bitter protests by union members to block the sell-offs.

Television footage showed crowds of workers staging sit-in protests outside the Delhi and Mumbai airports and threatening a strike.

Hundreds of policemen guarded the offices of India's civil aviation ministry as the bids were opened inside, reports said.

Plans to privatise the two international airports have been stalled for years amid opposition by workers fearing job losses.

India has offered 74 percent stakes in the airports where a lack of funds has stalled modernisation at a time when the airline market is expanding rapidly.