Plans to redevelop Mumbai's airport to cope with surging traffic could be held up by a 30 percent rise in the estimated number of squatters on the site.

The private developer charged with clearing the slums said there are 450,000 people, rather than 350,000 as originally thought, in shantytowns on land earmarked for the expansion.

India's economic boom has created a surge in domestic and international air traffic that overwhelms Mumbai airport, making its redevelopment a national priority.

The hovels around the airport are packed so closely that local folklore claims that children playing cricket in the slums can hit a six on to the tarmac alongside the runway.

More than half of greater Mumbai's estimated 18 million people live in slums, often on vacant government land originally reserved for new infrastructure projects or for expansion of existing facilities such as the airport.

The government has awarded an international consortium led by India's GVK and Airports Company South Africa the contract to increase the airport's capacity from 18 million passengers to 40 million and to build retail, hotel and other facilities.

The slum area, which occupies 276 acres of the 2,000-acre site, is possibly the biggest obstacle to the project.

Politicians and activists have warned that the slum dwellers' interests will be sacrificed for profit.

Earlier official estimates put the number of families living on the airport at 80,000 to 85,000, with four people per family. But most slum-dwelling families consisted of five to six members, resulting in his higher estimate for the total number of residents on the site.

In keeping with Mumbai's slum rehabilitation rules, the tenements would be provided free to each family and would be 225 sq ft each in size.