Workers in some subway stations in Beijing have started asking passengers carrying bottled drinks to take drink to prove they are not carrying banned liquids like petrol, local media reported yesterday.

China has intensified security measures at train and subway stations and airports after a flight crew foiled an attempt to blow up a plane over Xinjiang Uygur Autonomous Region in March.

Subway workers in Beijing were asking passengers to take a drink if "security equipment was unable to detect the content of the fluids in their bottles," The Beijing News said.

The city has introduced x-ray machines and sniffer dogs at subway stations to scan commuters' luggage.

Passengers will have to face security checks by machines, dogs or police officers at all subway stations from the end of June.

Yesterday's Beijing Morning Post quoted the city's public security bureau as saying the security measures will cover all operational subway lines and Line 10, which is yet to open.

The police called on passengers to cooperate, the newspaper said. It also published a hotline 008610-64011327 for information about combustible substances and explosives.

"It should be this way. If people with ulterior motives wear perfume and carry bottled petrol, then the security machines may not be able to detect them," a commuter said.

Others were less supportive.

"In summer, there will be a lot of people carrying bottled water but there are so many subway commuters ... If you make every person carrying a drink take a sip, it will just be chaotic," the Beijing News quoted an unnamed woman.

Police will also install security machines at busy bus stations.