LUOYANG, China (AP) _ Crying relatives on Wednesday scanned lists of victims from a Christmas night shopping mall fire that killed 309 people, as authorities questioned the building's operators and put them under surveillance.

With investigators uncovering a three-year history of safety violations in the building, Premier Zhu Rongji and Vice President Hu Jintao in Beijing ``ordered a thorough investigation into the cause of the fire and severe punishment of those responsible,'' China Central Television reported.

Most of the fire's victims came from an unlicensed disco on the top floor of the building, where hundreds of revelers at a Christmas party became trapped when smoke from the fire in shops on lower floors engulfed the club.

Police questioned 20 people connected to the fire and put them under close watch _ a status that could include restrictions on their movement _ state television reported, without identifying them. A spokesman for Luoyoung city said persons ``responsible for the building'' were among those questioned.

The government's response to the blaze in this central China city underscored its concern about popular dissatisfaction over rampant disregard for public safety.

The shopping center, called the Dongdu Commercial Building, was declared unsafe three years ago but never made fire safety improvements, the official Xinhua news agency reported.

The fourth-floor disco lacked fire prevention equipment and emergency exits, the report said. Though flames only reached the first-floor lobby, smoke rushed quickly up stairwells, suffocating trapped partygoers, Xinhua said. The floors below house businesses, including a new supermarket.

Of the two disco exits, one was filled with smoke and the other was hidden from view behind the bar, according to survivors cited by local newspaper Web sites. Smoke also prevented firefighters from getting inside, and panicked patrons hung out windows and balconies hoping for rescue.

Wang Weihong, an eyewitness quoted by the Southern Daily newspaper's Web site, said she and her boyfriend survived the fire by smashing the window in a private back room of the disco and were rescued by firefighters at 1 a.m., a half-hour after the fire was put out. Three others in the room succumbed to the smoke and died, the Web site reported.

The other victims came from a group of construction workers working on renovations elsewhere in the building. Construction workers in China often work around the clock, and at least 100 were at work when the fire occurred, the Southern Daily reported.

On Wednesday, scores of people filed into a makeshift government office in the downtown Luoyang Hotel for word on family members feared dead. Bodies were being kept at a morgue elsewhere in Luoyang, an ancient city located along the Yellow River.

Emerging from the building, one woman crumbled to the grass sobbing, after learning her 28-year-old brother was among the dead, a man accompanying her said. Hotel staff and police chased away reporters before the man could provide more details.

The subbasement where the fire apparently started housed a shop selling wooden furniture, while the supermarket on two basement floors above was planning to officially open on Dec. 28, the Web site said.

Investigators had not ruled out any causes, at least publicly. A Taiwanese Web site reported that a stray spark from construction workers welding in a sub-basement may have started the fire.

Authorities have turned up a history of delinquent management at the building, particularly over fire standards.

Provincial inspectors listed the building, leased to private managers, as one of the 40 most dangerous commercial outlets in Henan province in 1997, Xinhua said.

Luoyang authorities pulled the building's license to lease recreational space, but managers continued to rent out the fourth floor as a disco, the report said. Shop space was leased to private businesses without legal contracts, it said.

The managers recently signed a contract with a Taiwanese investor to make renovations, Xinhua said, and work was under way when the fire broke out.

The Luoyang city government spokesman, who spoke on condition of anonymity, confirmed the Xinhua report but refused to provide further details.

While officials stuck with a death toll of 309, other state media reports suggested there could be more. The Southern Daily's Web site reported that around 600 people were in the shopping center at the time of the fire, 500 of them in the disco, a figure based on ticket sales.

The Luoyang fire was the worst in China since the Dec. 8, 1994, fire in a theater the far western region of Xinjiang that killed 385 people, most of them children.