Toronto's downtown airport is expected to top year-over-year passenger estimates helped by more flights from the country's biggest airlines and improvements to the island airport.

The Billy Bishop Toronto City Airport, operated by the Toronto Port Authority, is seen surpassing its estimate of 1.5 million passengers for 2011, up 37 per cent from 2010. That is double the number of passengers it served in 2009.

And that number is expected to climb to some two million passengers in 2012, TPA spokeswoman Suzanna Birchwood told The Canadian Press.

The numbers were helped by increased service from the country's key airlines including Porter Airlines and Air Canada, the country's dominant airlines.

"Together with our airlines -- Porter and Air Canada -- we have made great strides in meeting customer demands for a quality travel experience," Geoff Wilson, president and chief executive of the Toronto Port Authority, said in a release.

Air Canada launched operations at Billy Bishop last May and now operates 15 flights a day from the island airport to Montreal, said Birchwood.

Five-year-old Porter, based at Billy Bishop, introduced service to Windsor, Sault Ste. Marie and Burlington, Vt., in 2011, and increased its number of flights to other destinations, including Ottawa, Sudbury, Thunder Bay, Mont Tremblant, Que., and Boston.

Earlier this year, Toronto City council approved a deal with the port authority for the construction of a pedestrian tunnel to the city's island airport.

Under the agreement, the port authority will have the right to use city waterfront land for the proposed passageway's construction. The deal also allows the city to install water supply and sewer infrastructure in the tunnel.

Plans for a link to the Toronto Island Airport have been in the works for a decade. There were once plans for a bridge to the airport which were scuttled when former mayor David Miller took office.

The pedestrian tunnel project advanced last February when the federal government moved to reverse a marine act amendment prohibiting "a bridge or similar fixed link" between the airport and the mainland.

Work on the tunnel, which is now expected to stretch 800 feet from the mainland under the Western Channel directly to the Airport Terminal building, is scheduled to begin in the spring.

With files from The Canadian Press