BEIJING - China's think tanks called on Monday for stricter steps to be taken to control the capital's fast-increasing population and said population pressures are likely to become stronger in the next 20 years.

Visitors swarm to the Tian'anmen Square in Beijing on May 1. Provided to China Daily

Population increases will be the biggest worry for Beijing administrators during the period covered by the municipality's 12th Five-Year Plan (2011-2015), according to the Annual Report on Analysis of Beijing Society-Building, also known as the Blue Book of Society Building, which was published by the Social Sciences Academic Press on Monday.

Since 2000, the population of the capital has increased by 700,000 residents a year on average.

That is putting strains on the economic, social and environmental resources of Beijing, the report said.

About 61.5 percent of Beijing residents live in six districts in the city's center, where the population density is at 7,837 persons for each square kilometer, according to the report.

Beijing's population density has surpassed London's - at 5,437 persons for each sq km - and Tokyo's - at 5,984 persons for each sq km.

By 2011, 40 percent of the Beijing population consisted of migrant workers who had been officially registered with the municipal government.

In a move to reduce the population pressure on the city, a series of strict limits are expected to be placed on new residents who are considered to be part of the "floating", or migrant, population.

For example, fewer university graduates in 2011 will get Beijing hukou, an official residence permit. The capital plans to only encourage those who have diplomas in fields deemed important to economic development to remain after graduation.

"High housing prices and increasing rental costs have automatically squeezed us out," said Li Yurong, a graduate from Hubei province who was looking for a job that would provide him a Beijing hukou.

"And we couldn't enjoy many public services without having a Beijing hukou."

He said the slogan, "Beijing welcomes you!", which was used during the 2008 Olympic Games in Beijing, is close to becoming ironic for many like him.

"In a move to reduce population pressures, Beijing should get 'low-end industries' and 'low-end workers' to leave the city," said Yin Zhigang, deputy director of the Beijing Administrative College's Beijing population and development research center.

"Some private universities, some hospitals (specially hospitals specializing in treating infectious diseases) and some official departments should also leave the capital," he said.

"Beijing hasn't set a concrete limit on what the population can increase to during the period of the 12th Five-Year Plan because the city failed to meet a previous plan's goal to keep the population within 18 million before 2020," said Liu Jinwei, a researcher with the Beijing University of Technology and the writer of the report.

He called on administrators to adopt policies that treat the floating population more humanely and to reduce population pressures by moving some industries into places around Beijing.