Five consortiums were initially pre-qualified to bid on the 13.8 trillion peso ($3.9 billion) project. The winner of the contract for the a 24-km (15-mile) elevated line will be announced on Oct. 21.

The metro, promised by city officials for decades, is considered key to taming traffic on Bogota's congested and chaotic roadways. It is meant to complement the city's Transmilenio system of buses.

One consortium is comprised of Mexico's Carso Infraestructura y Construccion and Promotora del Desarrollo de América Latina S.A. de C.V., Spain's FCC Concesiones de Infraestructura S.L.U. and Ferrocarril Metropolita de Barcelona and France's Alstom.

The second is comprised of China's China Harbour Engineering Company Limited and Xi'an Metro Company Limited and Canada's Bombardier.

"Bogota has guaranteed its metro - we have two proposals from formidable groups of international importance," Mayor Enrique Penalosa told journalists. "In April of next year work will start on the Bogota metro."

The winning consortium will have seven years to build the project and will operate it for two decades.

Colombia's capital, with some 7 million residents, will provide some 30% of the subway funding. The remainder will come from the national government.

(Reporting by Luis Jaime Acosta; Writing by Julia Symmes Cobb; Editing by David Gregorio)