Nature lovers are flocking to a valley in southwest China's Yunnan Province to witness the annual "butterfly explosion," when nearly 100 million butterflies from hundreds of different species emerge from their cocoons in a matter of a few days in a rare ecological spectacle.

Yunnan's Honghe Butterfly Valley is one of the only two places in the world where a butterfly boom of this grandeur can be seen, with the other in Mexico.

The first signs of this year's butterfly explosion were spotted on May 20, with the peak period happening in the last week of May, according to local officials.

More than 300 different species of butterflies appear during the explosion, the main one being the Stichophthalma, shaped and colored like a dead leaf. The butterflies will remain in the valley in such large numbers for about a month, wildlife experts say, giving enchanted butterfly lovers a real treat.

"We saw lots and lots of butterflies as soon as we got out of the car. Most of them were yellow like these," said one visitor.

The valley sits in a special climatic zone between the northern temperate belt and the south subtropical zone of China, and with an annual average temperature of 18 degrees Celsius and 67 percent forest coverage, it is the ideal environment for the butterflies that thrive here like almost nowhere else in the world.

"We estimate the number of butterflies this year will peak at around 80 million to 100 million. So far, about 70 percent have emerged," said Yang Zhenwen, curator of the Honghe Butterfly Valley Museum.

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