The fire that killed 19 people in Beijing's Daxing district on Nov 18 was caused by an electrical fault, ruling out arson, Beijing police said on Monday, and 20 people suspected of having liability for the conditions that led to the fire have been detained.

The fire broke out in a building with more than 400 residents in the village of Xinjian in Xihongmen township. Eight were injured in the incident.

The building, which has two stories in some parts and three in others and a basement, housed workshops and living spaces and was rife with safety hazards, officials say. A person identified only by the surname Fan began building the structure in 2002.

Fan began installing a refrigeration facility in the basement in March, and it was undergoing testing before the fire. The blaze was traced to a faulty wire in a wall built with flammable material. Fan was among those detained, police said.

After the fire, the city government launched a 40-day citywide campaign aimed primarily at eliminating fire hazards and other safety problems in crowded apartments and warehouses that function as storage areas, workshops or residences for workers.

Cai Qi, Party chief of Beijing, said in a meeting on Monday that removing all fire hazards takes time and cannot be accomplished within a short period, Beijing Daily reported. He also said it is necessary to draft a three-year plan to fundamentally solve the problem.

Cai urged authorities to be patient toward those affected by the government's efforts and give them more time to resettle.

On Monday, a job fair was held in Xihongmen to offer employment opportunities to people who lost their jobs when their employers were told to shut down unsafe factories or warehouses during the campaign.

More than 508 vacancies including driver, security guard and cleaner were offered by 27 companies at the job fair, and more fairs will be held in the area, the township government said.

Many warehouses in Xihongmen failed to pass fire and safety assessments and had to be closed. The fairs are mainly for those who became unemployed as a result, Chen Yongqiang, deputy head of the township, said at the job fair.

"For migrant workers who have decided not to work in Beijing anymore, we will provide temporary accommodation and train or bus tickets to go home," Chen said.

"We prefer the employers taking part in the job fair provide accommodation for employees," said Li Hualong, deputy head of the Daxing district human resource and social security bureau.

Zhao Chuanxin, 28, who had been working and living in a small clothing workshop in Xinjian where the fire happened, found a job at the job fair.

"The workshop was closed three days ago because of the campaign, so I had to find a new job and a place for me and my wife to live," said Zhao, from Shandong province. They have been staying in inexpensive hotels.

He signed a contract with a logistics company that provides meals and accommodation and soon he will start working as a driver. "I thought about going home but I am actually more familiar with Beijing," he said.