Photo taken on Nov. 15, 2010 shows an apartment building on fire in the downtown area of Shanghai, east China. [Xinhua]

Police detained eight people Tuesday in connection with Monday's blaze at a high-rise apartment building that left 53 people dead and more than 70 injured in Shanghai's Jing'an District, authorities said Tuesday evening.

An initial investigation has blamed the disaster, one of the deadliest in decades, on unlicensed welders, said Zhang Renliang, chief of Jing'an District Government, said at a press conference.

Some of the welders were among those detained, but the identities of the others were not immediately known.

Deputy district chief Li Weiping said 15 of the injured were still critically ill as of 4:00 PM.

The blaze erupted on the north side of the 10th floor of the 28-story building, said Chen Fei, director of the city's fire-fighting bureau.

The 85-meter-high building housed more than 156 households with 440 people. Residents moved into the building in March 1998 after construction was completed in 1997.

The building was undergoing an energy-saving renovation project when the fire started after lunchtime.

The Jing'an District Construction Corp. and Shanghai Jiayi Decoration Corp. were the contractors for the project.

The city's emergency response center received a fire report at about 2:15 PM and authorities dispatched 122 fire engines and more than 1,300 fire-fighters to the site.

More than 100 residents were rescued and the blaze was extinguished by 6:30 PM.

Local authorities are still trying to determine how many residents were in the building when the fire broke out and the number of missing people.

Police and fire-fighting authorities have promised to disclose more information about the cause of the blaze as soon as possible.

Horror scenes 

The entire building was engulfed in the fire and smoke for hours, with flames bursting out of the windows and cracking glass, witnesses said.

The scaffolding netting that enveloped the building quickly burnt and part of the iron structure turned red in the fire.

Among the residents were many retired teachers and some elderly people were in the building when the fire occurred as young people were at work.

Website pictures showed many residents climbing on to the scorched scaffolding, hesitating whether to jump.

A woman surnamed Lu thanked rescuers for carrying her 95-year-old father out of the building Monday. She also expressed gratitude to the local government for accommodating residents of the building in an adjacent hotels.

A man surnamed Wang said he ran all the way up and down twice to search for his wife and finally pulled her out of a burning room.

A woman surnamed Wang kept trying to call her husband and daughter, who were believed to be trapped in the building.

"She called me at about 6:15 PM, but I couldn't contact her and her father anymore. She is so young," the woman cried, collapsing to the ground.

An elderly woman living in the top floor of an adjacent building smelt the smoke first and saw parts of the scaffolding falling in flames. She carried her granddaughter down to the ground along with her husband, just before the elevator stopped working.

A young woman who gave birth two months ago was believed to be trapped in the building.

"I told her on the phone to protect herself with wet towels and quilts, but couldn't contact her again," said the woman's sister.

Many residents scrambled to the roof, but the flames were too strong for helicopters to lift them off.

Shanghai people began to mourn the victims Tuesday as some laid flowers at the site of the tragedy.

"I don't live in the block. I just came to express condolences," a man said without offering his name.

Safety loopholes 

The building was covered by scaffolding made of flammable nylon netting and bamboo, Chen said, adding that strong winds helped the fire spread.

Battling fires in high-rise buildings was difficult because flames could jump to nearby buildings, he said.

Experts said fire-fighting capabilities in many Chinese cities were inadequate for fires more than 60 meters above ground level. People had to help themselves in higher buildings, said Wang Wuren, a leading architect and former chief engineer of China State Construction Engineering Corporation.

"The highest aerial ladder apparatus in China is not more than 100 meters, but there are almost 1,000 buildings more than 100 meters high in Shanghai alone," Wang said.

In some big cities, fire engine access had been squeezed, leaving many sites unaccessible, Wang said.

Li Jin, deputy director general of Beijing Fire Bureau, said helicopters would be restricted by the smoke, heat, strong winds, and crowded space during the rescue process.

"According to regulations, a fire station must be set up every four to seven square kilometers, but rapid urban expansion makes it hard for fire control facilities to catch up," Li said.

Li suggested spacial and regional plans should be considered during the urban planning process to avoid further tragedies.

"Enough space should be reserved for fire control emergencies, especially around high-rise buildings," he said.

Li said Beijing had purchased a fire appliance that could extend to 90 meters high for the Olympic Games, and after the fire at the China Central Television (CCTV) headquarters in 2009, another that could reach 101 meters was ordered and would soon be put into use.

In addition, many residential buildings provided too few or ineffective safety facilities and the maintenance work was inadequate. Fire control authorities in other provinces and cities, such as Tianjin, Guizhou and Zhejiang, Tuesday started inspections of facilities in a bid to prevent similar occurrences.