Reporting from Changsha, China — In early December, Liu Zhangning was tending her cabbage patch when she saw a tall yellow construction crane in the distance. At night, the work lights made it seem like day.
Fifteen days later, a 30-story hotel towered over her village on the outskirts of the city like a glass and steel obelisk.
"I couldn't really believe it," Liu said. "They built that thing in under a month."
A time-lapse video of the project in Changsha, which shows the prefabricated building being assembled on site, has racked up more than 5 million views on YouTube and left Western architects speechless.
"I've never seen a project go up this fast," said Ryan Smith, an expert on prefabricated architecture at the University of Utah.
In other countries, the most advanced prefab construction methods can reduce building times by a third to half, Smith said. The builders of the Changsha hotel did better, knocking one-half to two-thirds off the normal schedule.
"It's unfathomable," Smith said.
The warp-speed construction is a startling illustration of the building boom in China, where an exodus from the countryside to the cities has swelled the urban population by almost 400 million since 1990.
Skylines are peppered with cranes. Smog-choked streets echo with the pounding of jackhammers. Residential high-rises sprout like weeds in the plains between major cities, creating an endless sprawl along the country's east coast.
The breakneck pace of construction reflects a societal urge to catch up as fast as possible to the developed world after decades of scarcity under Mao Tse-tung, said Zhang Li, a Beijing architect.
The focus on fast construction took root during the economic reforms of the early 1980s, Zhang said. Prefabrication methods, well established elsewhere but just catching on in China, have magnified it.
Raising a 30-story tower in two weeks is possible because most of the work is done in a factory and the foundation has been laid ahead of time.China'sabundance of workers also helps.
But a job done quickly is not always a job done well. Zhang said that in their race to the finish line, many Chinese construction companies skimp on the meticulous reviews and inspections that make projects in the West drag on for years.
"Incredible speed also means incredible risk," he said. "But only time will tell how serious the risk is."
The Chinese company behind the Changsha hotel, Broad Sustainable Building, says it cuts no corners on safety. To the contrary, it says, its methods will makeChina'sconstruction boom safer, cheaper and more environmentally friendly.
In promotional literature, Broad boasts that its technology is "the most profound innovation in human history" and that construction on a third of the world's new buildings will be done this way "in the near future."
The hotel, called T-30, looms over dilapidated concrete homes interspersed with piles of garbage and rows of cabbages and leeks. Dogs and chickens run through muddy alleyways.
In mid-January, a month after the building's announced completion, its interior was a hive of activity. Many of the 500 rooms were finished, with made beds and white sofas. In others, wires protruded from unfinished walls. Paint-splattered workers hauled wooden planks past a grand piano in the pristine marble lobby.
The hotel, which will accommodate visiting clients of Broad Sustainable Building and house some of its employees, is about 400 yards from the cavernous white factory where its components were manufactured. The headquarters of the parent company, Broad Group, is a 90-minute drive away.
"This is the tallest building in this county, and it's also the fastest-built," said Rong Shengli, one of the building's planners, looking over the rural sprawl from a helicopter pad on the hotel's roof. "Next we're going to build a 50-story building. Then a 100-story one, then a 150-story one. And they're all going to go up fast."
The time-lapse video provides a glimpse of how the hotel was made. Workers in blue jumpsuits are seen assembling "main boards," the building blocks of Broad's structures -- 13-by-50-foot slabs containing ventilation shafts, water pipes, electric wiring and lighting fixtures sandwiched between ready-made floors and ceilings.
A counter at the bottom of the screen ticks off the hours as the boards are loaded onto a truck and delivered to the construction site. A crane then stacks them up like blocks. Workers bolt in pylons and piece together staircases; the glass and steel exterior rolls up onto the frame like a gleaming carpet.
At 360 hours, the ticker stops.
Building this way costs 20% to 30% less than traditional methods, said Jiang Yan, a senior vice president at Broad.
It's also safer, said Zhang Yue, chief executive of Broad Group, because factories are typically less risky environments than construction sites.