ST. PETERSBURG - A nine-story apartment building collapsed Monday in St. Petersburg, killing at least one person and leaving more than 400 homeless. Clouds of dust hung over the heap of bricks and smoking furniture that once was their home.

According to rescuers' documents, seven of the 413 people registered to live in the workers' dormitory remained missing as of midnight. Two were children, and one was a woman who had reportedly called a relative from under the ruins asking for help.

Andrei Bagotsky, head of the rescue effort, said one man was found dead of apparent suffocation in the collapse, which buried cars and sent up giant clouds of dust and black plumes of smoke from a fire that also hit the building.

Anna Markova, vice governor of Russia's former imperial capital, said she "could not rule out" that people could be trapped inside, but added, "There were at least 20 to 30 minutes for them to leave the building."

Rescue workers said they were first alerted to a crack that appeared suddenly in an upper apartment in the boxy apartment building, and about 55 people were evacuated. Each eight-room apartment housed several families who shared a kitchen and bath, a common Soviet construction solution to housing shortages.

Within an hour, the top three floors of the building collapsed, and then part of the building burst into flames.

As residents huddled outside under rainy skies, the entire building buckled and crumbled to the ground.

"I was taking a shower in the bathroom, when I heard something like an explosion. The bath shook under me, and the ceiling cracked," said Yuri Pchelintsev, 18, who lived on the seventh floor.

"I rushed to open the bathroom door but it was stuck. So I broke the little window in the bathroom and climbed out through the hole," he said.

Nadezhda Tolmacheva said she was at home with her 8-year-old daughter when she noticed a crack in the ceiling. She took her daughter and rushed downstairs, climbing to safety by way of a firefighter's ladder.

Officials said four people were taken to hospitals, one with cuts from broken glass, one with heart trouble, and others with breathing problems.

Residents speculated that maintenance on the building's water pipes that began Monday morning could have been at fault. Police and firefighters said a gas leak or explosive device were also possibilities.

Emergencies Minister Sergei Shoigu, who arrived at the site Monday night, said maintenance work with welding equipment may have been to blame.

Meanwhile, St. Petersburg police defused an explosive found in the entry way of another city apartment building on Monday. The device was equipped with a timer but had no batteries, and police spokesman Elmar Shakhirzayev said it was likely being stored in the building.

Aging infrastructure has led to many accidents in Soviet-era state-built apartment blocks, which house a large portion of Russia's population. St. Petersburg has seen four apartment buildings collapse in the past four years, but none resulted in casualties until Monday.

Vladimir Yakovlev, governor of St. Petersburg, said on Inform TV that he ordered that all those who lost their homes be provided with new apartments. Until then, the residents will live at a nearby kindergarten or school.