A tenant carries his bedclothes away from a basement room in Beijing's Shijingshan district on Friday. More than 50 migrant families lived in 170 rooms that had been illegally constructed in a basement area the size of a soccer field. Public security, fire protection and administration authorities cleaned up the units.[Wang Yixuan / For China Daily]

Beijing has called for the illegal construction of basements to be stopped after such work caused neighboring houses and part of the road surface to collapse in the city, forcing 15 people to be evacuated.

A government office that oversees construction work in Beijing said in a statement on Sunday that the municipal government will fill in basements or holes caused by illegal construction work.

It will do so when property owners refuse to restore homes to their original condition within three days of being ordered to do so.

The office said carrying out renovation work that is more than 1 meter deep without permits in residential areas constitutes illegal construction and is an offense.

The collapse and its aftermath have highlighted rampant underground construction at houses with courtyards by unscrupulous billionaires and those seeking to cash in on providing underground shelters for low-income people in the city.

"It is almost impossible for the city's planning authority to issue a permit for basement construction to private owners of houses with courtyards,"said Gui Lin, an agent at Hong Guan Real Estate, a company that focuses on courtyard sales and reconstruction.

"But real estate companies can always find ways to complete the construction, calling it a 'renovation'."

Gui said his company has been involved in the renovation business for more than 10 years and has good connections with the city's law enforcement departments.

The company has about 40 homes with courtyards on its books. The smaller ones occupy about 100 square meters and cost a minimum of 10 million yuan ($1.6 million). He said the company charges 5,000 yuan per square meter for renovation work.

Beijing's Urban Planning Commission said the collapse happened when a basement 18 meters deep was being dug at a house with a courtyard on Deshengmennei Street. A construction permit had not been obtained.

Liu Yunzhi, who lives across the street from the house, said people living nearby had filed complaints to law enforcement authorities in vain.

The owner of the house, a legislator in Xuzhou, Jiangsu province, who is president of a local company, resigned from the lawmaking body after the incident.

Beijing Daily reported that three workers died in July 2010 at the Deshengmennei Street house during illegal basement construction work after the legislator bought the property in April that year.

A real estate agent, who requested anonymity said, "The unauthorized construction in courtyard houses is rampant in Beijing. Owners want to expand the space and increase the value of their houses."

The agent said most of the owners are wealthy and don't care about spending money on basement construction.

"They may have friends in the government, making them immune from neighbors' complaints,"he said, adding that this explains why illegal construction is hard to stop.

Beijing News reported that work on a 3-meter-deep basement at a 500-square-meter house with a courtyard in eastern Beijing had continued illegally after the city authorities made their crackdown announcement on Sunday.

A worker at this site said the reconstruction work would be completed in June and the property is expected to be listed for sale at 60 million yuan, the report said.

Beijing has traditionally used underground space.

In Wangfujing Street in the center of the city, underground air raid shelters are used for business, shopping and entertainment centers. In the west of the city, a bunker has been converted into a wholesale market with about 1,000 stalls.

In recent years, underground shelters have become homes for many low-income earners in the capital.

This week, media reports said that following the recent collapse 55 families living in more than 170 rooms built on the site of a former fishpond occupying 1,500 square meters had been asked to evacuate.

Wang Wei, an official at the city's construction watchdog, said it is an offense to start basement construction work without obtaining a permit.

The government office urged owners to stop illegal underground construction work immediately and restore houses to their original condition.