China ordered tighter fire prevention measures Wednesday following a blaze that gutted a high-rise apartment building in Shanghai, killing at least 53 people with dozens still believed missing.

The fire heightened concern over the ability to cope with such disasters in this city of 20-plus million people, many of them living in its 15,000 high-rise buildings.

Relatives continued to search for loved ones, while authorities have not given any figures for the number of missing from the fire in a downtown neighborhood Monday afternoon.

Shanghai's fire chief, Chen Fei, said firefighters searched the 28-story building thoroughly after the fire was put out and could not have missed anyone.

"Sleepless night for victims, every minute caught between hope and despair," said a headline in Wednesday's edition of the local newspaper Oriental Morning Post.

As might be expected of a weekday afternoon, many of those in the building at the time of the fire were retirees.

A media officer at the city's information office said tests on victims confirmed the identities of 26 of the 53 people killed in the disaster, contradicting a report by the official Xinhua News Agency that said the 26 were in addition to that death toll. The official spoke on condition of anonymity, in keeping with government rules.

Police detained four unlicensed welders who were working on "energy-saving" renovations when sparks from their welding apparently spread to bamboo scaffolding and nylon nets shrouding the building. The city's deputy police chief, Cheng Jiulong, said eight people had been detained, but did not identify them.

Chen, the fire chief, sought to deflect public outrage over the government's handling of the disaster, saying firefighters had done the best that could be expected given the height of the building and amount of flammable materials that caught fire.

In a notice posted on its website, the Cabinet ordered authorities to improve fire safety and prevention, especially in the winter when widespread use of space heaters is an added risk. It named construction sites and high-rise buildings as areas needing extra attention.

Shanghai recently hosted the World Expo and is still in the midst of a construction frenzy that has brought new subway lines, highways and airport upgrades. The city is one of China's best-run, but its public services still lag far behind its often ultramodern infrastructure.

Unsafe building work remains a chronic problem in China. Last year, a nearly finished 13-story apartment building in Shanghai collapsed, killing one worker. Investigations showed that excavated dirt piled next to the building may have caused the collapse.

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Associated Press researcher Ji Chen in Shanghai contributed to this report.