A massive search and rescue operation is under way in south-western China after one of the most powerful earthquakes in decades.

Troops have arrived in Wenchuan county at the epicentre, which was largely cut off by the quake - but heavy rain is hampering rescue operations.

Elsewhere in Sichuan province, frantic efforts are being made to reach thousands of people under the rubble.

The death toll is now more than 12,000, officials say, and looks set to rise.

In one city, Mianyang, near the epicentre, more than 18,000 people are said to be buried under the rubble and 3,629 have been confirmed dead, state news agency Xinhua reports.

Unless more access to the country is granted to allow aid more quickly, a second catastrophe could result, Elizabeth Byrs of the UN Office for the Coordination of Humanitarian Affairs (OCHA) said in Geneva today.

Despite some progress, efforts to help the 1.5 million people impacted by Cyclone Nargis must be enhanced, she observed. Some 12 days after the cyclone stuck Myanmar, the UN and its partners have reached 270,000 at-risk people, less than a third of those affected. Heavy rains have been forecast, further impeding aid efforts, Ms. Byrs noted. She called for an air and sea corridor to channel aid in large quantities as quickly as possible.

The official death toll reported by the Government has reached almost 32,000, with over 34,000 others missing.

Yesterday Secretary-General Ban Ki-moon voiced his “immense frustration” with the slow pace of relief efforts and called on the South-East Asian nation’s authorities to do the most it can to prevent the situation from deteriorating further.

About 300 tiny Kihansi spray toads live in a small room at the Bronx Zoo in New York as part of a captivity breeding experiment. The toads lived in a small river gorge in Tanzania until a few years ago, but now they are completely extinct in the wild.

The Kihansi toads are part of a conservation program aimed at protecting the thousands of amphibian species that face unprecedented threat of extinction. The global effort, known as the Amphibian Ark, plans to keep 500 species in captivity at zoos and breed enough to eventually reintroduce them into the wild.

“In terms of scope, I think this is the biggest conservation project that humanity has ever tried to tackle,” said Kevin Zippel, the program’s director, who said the initiative is testing zoos’ ability to raise and maintain animals with specialized needs. “In the course of the last four years, we’ve realized how badly off amphibians are.”