Luong Thai Linh / EPA
Smoke billows a blazing building in Hanoi, Vietnam, on Thursday.
Updated at 11:20 a.m. ET: At least 30 workers were rescued when an office block being built by Vietnam's state power company caught fire Thursday, engulfing part of downtown Hanoi in black smoke.
Several workers waved their shirts from an upper-floor balcony to call for help after smoke began to engulf the building, The Associated Press reported. Others used cellphones and flashlights to summon help. At 10:15 p.m. local time (10:15 a.m. ET), it was not clear whether any people remained trapped in the complex, which was described by local media as the city's "twin towers."
However, Tuoi Tre News reported that "all people trapped in the towers had been rescued."
The official Vietnam News Agency said 30 workers were rescued, including 16 who were hospitalized for smoke inhalation.
Witnesses said they saw flames in the basement of the 33-story building. The Thanh Nien newspaper quoted Nguyen Huy Hoc, a worker who escaped the blaze, as saying sparks from welding in the basement ignited nearby material in the air-conditioning system.
Published at 9:10 a.m. ET: About 20 people were believed to be trapped Thursday after a blaze broke out at a skyscraper in the Vietnamese capital of Hanoi, according to reports.
Tuoi Tre News reported that clouds of smoke billowed from the under-construction EVN Center for Telecommunications Information Management after the fire started around 4:30 p.m. local time (4:30 a.m. ET). Citing a source, it said at least two people had been rescued and taken to hospital from the "twin towers" complex.
Tuoi Tre quoted an official as saying that some workers on the site "rushed to upper floors" when the fire erupted.
According to BBC Vietnam, about 20 people were believed to be trapped inside.
The BBC reported that one of the buildings is 33 stories, while the other has 29 floors.
It added that either a gas explosion or faulty wiring was believed to have sparked the blaze.
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The Associated Press and msnbc.com staff contributed to this report.