Opium cultivation in Southeast Asia has doubled over the last six years as growing demand for heroin in China and the rest of Asia lures more farmers to grow poppies, the UN said Wednesday.

Opiate users in East Asia and the Pacific now account for about a quarter of the world total, the UN Office on Drugs and Crime said in a report.

China alone has more than a million registered heroin users, and consumes most of the drug in the region, it said.

With prices rising, cultivation in Laos soared 66 percent to 6,800 hectares (16,800 acres) in 2012, and by 17 percent to 51,000 hectares in Myanmar, the world's second largest producer after Afghanistan, according to UN estimates.

"Overall, opium poppy cultivation in the region has thus doubled since 2006," despite officials reports from Laos, Myanmar and Thailand that nearly 25,000 hectares of poppies were eradicated in 2012, the report said.

The study estimates opium produced by Laos and Myanmar to be worth $431 million in 2012, a third more than the previous year. Farm-gate prices per kilogram reached $1,800 ($820 a pound) in Laos amid scarce supply, and $520 in Myanmar.

The number of people engaged in cultivation has risen in parallel with up to 38,000 "opium growing households" in communist Laos and 300,000 in Myanmar.

The rise indicates Myanmar farmers -- mainly in northeastern Shan state -- will only turn away from opium cultivation if alternative livelihoods are available, the report said.

"Farmers are very vulnerable to losses in income derived from opium, especially those who depend on such an income source for food security," it said.

"Furthermore, opium cultivation is generally linked to the absence of peace and security, which indicates the need for both political and economic solutions," it added, referring to conflict in opium-producing Kachin state.

Myanmar has followed a 15-year-plan to eradicate opium by 2014, but the UN study, which used satellite, helicopter and ground surveys, suggests the target is falling away.

In September the United States kept Myanmar, which is undergoing a series of political reforms after decades of military rule, on its drug trafficking "black list", accusing it of having "failed demonstrably" to fight the drug trade.