BEIJING, May 26  -- Beijing police have deployed helicopters for daily air patrols of the city as a new measure to tighten security, the Beijing Municipal Public Security Bureau announced on Monday.

Since Saturday, five police helicopters have patrolled eight routes covering transport hubs, shopping centers and scenic spots two or three times every day. They will also patrol major highways and crowded areas, said Yang Dongfeng, head of the bureau's air patrol corps.

The helicopters will hover and observe any suspicious situations. The pictures they take will be sent back to ground command center in real time, Yang explained.

The aircraft will also be able to apply air support if necessary, he added.

Subway security checks were also tightened on Saturday. In January, Beijing Subway began requiring passengers to go through airport-style full-body scanners at six stations, all near Tian'anmen Square in central Beijing.

The system has now been introduced in three more stations -- two in the city's north and one in the west -- all far from downtown, according to Beijing Subway.

The new security measures come as Beijing and the country at large are on high alert in the wake of a spate of terrorist attacks.

A bombing at an open air market in Urumqi, capital of far-west China's Xinjiang Uygur Autonomous Region, left 39 people dead and 94 others injured on Thursday. That followed a string of violent attacks, including one at a train station in the southwestern city of Kunming in March and another in Beijing's Tian'anmen Square in October last year.

Authorities in Beijing have launched several anti-terrorist drills over the past month, in a bid to tighten the capital's security.