Guangzhou's government has launched a month-long safety inspection campaign across the city targeting factories, offices, residences and parking lots located 30 meters either side of an expressway.

The move is to prevent serious accidents like Friday's explosions, which killed at least 20 people and injured 31. The explosions were triggered by solvent oil that leaked from a rear-ended tanker truck.

The solvent oil flowed down to the drain under the Nangang section of a flyover along the Yanjiang Expressway, then caught fire and burned buildings and a container yard. The tanker truck was carrying 40 metric tons of solvent oil.

Most of the people killed were sleeping in a wood products market under the flyover, according to those who escaped from the fire.

The accident exposed the loopholes in some of the local governments' supervision of buildings near expressways, said the Work Safety Committee Office of the State Council in an announcement posted on Monday on its website.

According to road safety regulations, local governments have to rope off areas at least 30 meters from the fringes of expressways as a control area. It's forbidden to set up new buildings in those areas after the areas are roped off, unless the buildings are to protect the expressways. Any illegal buildings in those areas also have to be bulldozed.

Under the expressway in Guangzhou where the tanker truck was rear-ended there was a container yard and the wood products market, both with significant quantities of combustible materials.

Luo Pan, 18, one of the people working and living in the wood products market, said that the buildings there were temporary and mainly made of bamboo. He added that none of the wood processing factories had a business license.

"The explosions would have caused fewer casualties if there wasn't the wood products market and the container yard under the flyover," said Zhao Shaohua, a lawyer at the Guangdong Chuangji Law Firm.

Zhao added it is worrying that there are buildings such as restaurants, garages, parking lots and even dormitories for sanitation workers under the expressways in Guangzhou.

"With buildings under the expressways, people will suffer bigger losses in terms of property and personal safety once an accident such as an expressway's collapse takes place," Zhao said.

The accident in Guangzhou on Friday also sounded an alarm bell for Song Shoulong, the 28-year-old owner of a garage under a flyover in Hanjing Road, Tianhe district, along the South China Expressway. After the accident, he examined the 15 fire extinguishers in his garage and replaced some.

Song took over the garage from the previous owner two months ago. He believes that the garage is not an illegal building.

"The previous owner said the garage has been here for four years and is registered with the local administration for industry and commerce and the tax department," said Song, showing the garage's business license.

"The owner of the land is the Vegetable Research Institute of the Guangdong Academy of Agriculture Sciences. They allow me to rent the space for the garage. I'm paying 25,000 yuan ($3,900) a month to the institute to rent the 500-square-meter space," Song added.

There are another three garages under the expressway.

"It's difficult to find another place to build a garage besides the space under a flyover. The rent for an open space in a business or residential area will be much higher and the noise produced by a garage will disturb people," said Song.

Zhao added that people are being allowed to use the open spaces under the flyovers due to limited urban land resources.

Contact the writer at xujingxi@chinadaily.com.cn