A business owner transports mannequins on Tuesday in Xinjian village of Beijing's Daxing district, as the village demolishes illegal buildings in the wake of a deadly fire that claimed 19 lives on Saturday. WANG JING/CHINA DAILY

People who died in a fire in the Beijing's Daxing district were poisoned by carbonic oxide from a newly installed underground refrigeration facility, authorities said.

None of the 11 workers working on the refrigeration facility, including those wiring the electrical circuits and debugging the facility, were professionally qualified for their jobs, the local government said.

The blaze, which occurred in an apartment building with more than 400 residents on Saturday night, killed 19 people and injured eight others. Six of the injured who were hospitalized have been discharged. The police are still investigating the cause of the fire, district officials said at a news conference on Thursday.

Of the victims, eight were under 18 years old, with the youngest just 1 year. The oldest victim was a 60-year-old male. Most of the victims were from Shandong, Henan and Hebei provinces, which are home for many migrant workers.

The building, with a total floor space of 20,000 square meters, has two floors above ground in most parts and three in another part－plus a basement. A person identified only as Fan started building the structure in 2002.

Fan began installing the refrigeration facility in the basement in March. It was undergoing testing before the fire.

The police detained the refrigeration workers, as well as seven people who managed the apartment block.

Disciplinary watchdogs at the city and district level established a joint investigation group on Sunday, dispatching five teams to government departments to collect evidence. The group is also coordinating with the police to investigate how the building could have been built and used without any government objections, the authorities said.

Beijing ordered a 40-day citywide safety check following the fire.

Cai Qi, Party chief of Beijing, demanded that inspectors comb the capital inch-by-inch.

He also called for the rooting out of unqualified industrial compounds used for illegal business operations in rural areas of the city to ensure safety.