Ranger police with guns and armor started to patrol Shanghai's two airports yesterday to reinforce security before the 2010 World Expo, police announced.

It's the second time for this kind of security beef-up in the city, the first being a short trial during the Beijing Olympics in 2008.

This time the step up in security will be in place for a long term, as it is in many international airports, according to Shanghai Public Security Bureau.

The ranger police officers, together with police dogs, will cover every terminal building and street around Pudong International Airport and Hongqiao International Airport.

"Our patrol team is on 24 hours standby," said Wang Qianyi, a commander of the team. "We will mainly handle the unidentified and suspicious objects and emergencies."

The regular security patrol will also be kept and maintained, police said.

"The patrol of the ranger police this time is different from the one during the Olympics," said an officer surnamed Sheng.

"It will be longer and will be continued as a regular patrol system after the World Expo."

Shanghai now has its ranger team patrolling in airports, along with other big cities such as Beijing, Hong Kong and Singapore, Sheng said.

Meanwhile, the city will organize five drills from April 20 to 25 at the Expo site after the site runs a pilot operation on April 15.

Construction trucks are one of the major targets during the checks, the huge vehicles having caused over 20 deaths last year as construction speeded up before the event.

More checkpoints will also be set at ramps of expressways.

"Safety is one of our biggest concerns during the Expo," said Shanghai Vice Mayor Shen un,

"It's a key to the success of the event."