Authorities Monday shut down Mexico's -- and possibly the world's -- biggest garbage dump and said they would invite bids to exploit methane gas generated by the decomposing waste.

Waste Management Commission chief Fernando Menendez called the closing "historic" as "it is the world's largest (truck-filled open-air) dump."

The Bordo Poniente dump for years saw 200-250 trucks a day cast off their waste -- up to 6,000 tons a day at its peak. Dumping had slid recently to some 2,800 tons a day, as it neared capacity.

Mexico City Mayor Marcelo Ebrard was on hand for closing day, and insisted that using the methane gas offset was key.

"A statement was published today that will allow us to open up bidding internationally," said Ebrard. "If the gas is not used, our goal is not achieved, which is to reduce gases being emitted into the atmosphere."

The dump, thought to hold millions of tons of compressed waste, towers over 17 meters high.