The helicopter hovered for an hour on Saturday over rugged hills about 70 km (45 miles) northwest of the city, transmitting video images back to police headquarters, the official Xinhua news agency reported on Sunday.

The search drew a blank. The police plan to scour several other remote areas over the next two weeks, according to the Beijing News.

It's a crime in China to grow more than 500 poppies, which are used to make heroin but are also a source of medicinal ingredients.

'Some poppy growers, who plant poppies to make drugs, always choose the remote and sparsely populated areas at the border of Beijing and the neighbouring Hebei province,' Xinhua quoted Zhao Wenzhong, a senior officer with the Beijing Municipal Public Security Bureau, as saying.

China was the world's leading opium producer in the early 1900s. Today, more than 90 per cent of the drug comes from Afghanistan. -- REUTERS