Beijing beefed up security in the city's metro on Tuesday while Shanghai reported preparations for the World Expo meant thousands of police were already safeguarding its underground, said China's senior public security officers.

Fu Zhenghua, director of the Beijing Public Security Bureau, confirmed the security in the capital city had been increased after the double suicide?blasts in Moscow's subway Monday.

"Police patrols aided with sniffer dogs were increased at metro stations, where police would make more frequent inspections and cross-question suspicious passengers," he said.

He added that Beijing had maintained tight transit security since the 2008 Beijing Olympics.

Song Youguo,director of the Operation Center of the Rail Branch under Shanghai Public Security Bureau told Xinhua on Tuesday, Shanghai had a very tight security regime with 10,000 police monitoring the city's metro system, as well as 400 security staff, in preparation for the upcoming World Expo.

Metro security checks were aided by dozens of bomb sniffer dogs, he said.

Shanghai's metro handles about 5 million passengers a day and an estimated 800,000 more after the Shanghai World Expo starts on May.1.