Construction on the world's largest optical telescope began Friday on a mountain in the Atacama Desert in northern Chile.

With a main mirror measuring 39 meters in diameter, the telescope is to explore exoplanets outside the solar system on which there could be life. The telescope, which belongs to the European Southern Observatory (ESO), is to be operational in the year 2024.

Known as an ELT, which stands for "Extremely Large Telescope," it is being built on the 3,048-metre-high Armazones Mountain 130 kilometers south of Antofagasta.

The ELT will have four other mirrors beyond its main mirror, which will have approximately 800 hexagonal sections, each with a diameter of 1.4 meters.

The casting of the ELT's secondary mirror was forged in Mainz, Germany. With a diameter of 4.20 meters and a weight of 3.5 tons, it is the largest secondary mirror used on a telescope and the largest-ever produced convex mirror.

"More than one telescope is being built here: it is one of the largest exhibits of the possibilities of science and technology and the potential of international cooperation," Chilean President Michelle Bachelet said Friday at the groundbreaking ceremony.

The construction of the ELT puts Chile on the way to becoming the home to 75 per cent of the world's astronomical observation capacity.

The ESO, which was founded by 15 European countries and Brazil, has its headquarters near the German city of Munich. It oversees three other observation locations in the Atacama Desert.