SHANGHAI » Thousands of somber Chinese marked a traditional day of mourning Sunday for 58 people killed in a high-rise fire in a gathering closely watched by police.

Police were grabbing people by their collars and pulling them away from a designated mourning area if they tried to enter without carrying flowers. People at the scene said there appeared to be no sign of protest, though some groups of agitated locals were discussing the fire and its causes.

China’s officials are highly sensitive to any mass, emotional gathering that could swing into anger and social unrest.

The fire swept through the 28-story building Monday after sparks from welding equipment set alight nylon construction netting and bamboo scaffolding. Some people scrambled down the scaffolding to escape.

The Shanghai government said most of the victims died inside their own homes, overcome by smoke, toxic fumes and heat.

Another 71 were injured, and an unknown number of people are still unaccounted for.

"Shanghai Don’t Cry: Mourn the Victims of Shanghai’s Jiaozhou Road Fire," said small black-and-white posters being handed out by some young people wearing badges that identified them as "volunteers."

Anguished family members and others angry over the government’s handling of the disaster are demanding answers.

Wang Yinxing, a resident of the building whose wife Wang Hao died in the fire, said by telephone that he and other survivors were not at the site Sunday because they were "not in the mood.

"The rescue was not timely or helpful enough," he said. "I don’t believe anything the government says."

The seventh day is a traditional day of mourning in China, and the authorities seemed prepared for Sunday’s large showing. Quiet crowds filed past the building, which was blocked off by police baricades. Just before the building was a huge pile of flowers, stuffed animals, photos of victims and offerings of cigarettes.

China’s work safety chief has blamed the fire on illegal contracting, unsafe materials and poorly supervised, unqualified workers. The official Xinhua News Agency said police have detained 12 suspects, including four welders who were allegedly working without proper qualifications.

Shanghai’s top officials bowed three times in a silent tribute and left flowers at the fire site early Sunday, the China News Service reported.

A man surnamed Li answering the telephone at the main office for Shanghai’s downtown Jing’an district, where the fire occurred, confirmed that the leaders made no public comments. He called the day’s events orderly. District police did not comment.

"We feel deeply about this," Shanghai’s Communist Party chief Yu Zhengsheng told victim’s families on Friday, the Beijing Times reported. "We’ll do our best to help you overcome your difficulties."

The fire has raised alarm over China’s widespread efforts to meet energy efficiency targets by adding insulation to the outside of existing buildings — the project the welders were working on when the fire broke out.

Although the insulation meant for such work is supposed to be treated with fire retardant, it is nonetheless flammable. Many are now questioning if the energy savings are worth the risk.

Beijing, China’s capital, has ordered projects similar to the one struck by the fire stopped, pending reviews and "rectification" of any problems.

But officials in the district where Monday’s fire occurred said such projects would continue.

Unsafe construction work is a huge problem for China, and residents of the destroyed Shanghai building complained that workers, lacking qualifications and working illegally for unlicensed subcontractors, were smoking on the job and leaving flammable materials piled up on the scaffolding.