Shanghai and the nearby coastal province Zhejiang have evacuated 456,000 people as China prepares for its third typhoon in less than a week.
The emergency measures were taken after Typhoon Haikui turned Manila, the Philippines capital into "waterworld", killing 50 people.
The typhoon is expected to make landfall in Zhejiang province, just south of Shanghai, late Tuesday or early Wednesday, the China Meteorological Administration said.
Shanghai officials fear the storm could be the worst since 2005, when Typhoon Matsa killed seven people in the city, state media said.
The city aimed to move 200,000 people to more than a hundred shelters by Tuesday evening, government officials were quoted as saying.
The Shanghai government ordered outdoor construction sites shut down and cancelled summer classes for children until the typhoon had eased.
Authorities in Zhejiang were also rushing to get people out the path of the storm, with 256,000 residents of the province evacuated so far, state media said.
More than 30,000 ships had rushed to shelter in ports.
The typhoon was packing winds of up to 151 kilometres per hour and could bring up to 400 millimetres (16 inches) of rain to some areas, it said. The eastern provinces of Jiangsu and Anhui would also be affected. China is still recovering from Typhoons Damrey and Saola, which hit over the weekend. Those storms brought heavy rains that killed 23 and left nine missing.
Xinhua said the heavy rains that came with the typhoons triggered mudslides and flooding, affecting hundreds of thousands of people.
Typhoon Haikui's torrential rains submerged much of the Philippine capital and surrounding areas on Tuesday, forcing nearly 270,000 people to flee their homes with more flooding expected in the north of the country as a tropical storm passes through the region, officials said.
Steady rains for the past 10 days, killing more than 50 people, are set to continue until Wednesday, the Philippines weather bureau said.
"It's like Waterworld," said Benito Ramos, head of the Philippines national disaster agency, referring to a Hollywood movie about a flooded world.
Schools , financial markets, and public and private offices were ordered shut, including outsourcing firms whose corporate clients are mainly from the United States and Europe.
Disaster officials said over half of Manila was swamped by floods as high as three metres, worsened by a high tide and the release of water from dams in surrounding provinces.
President Benigno Aquino, in an emergency meeting briefly interrupted by a power failure at the main army base in Manila, ordered officials to exert maximum effort to aid residents in flooded areas. Officials have deployed army troops, police and emergency workers with rubber boats and amphibious trucks.
The monsoon rains, which dumped about 300 mm (12 inches) or three times the daily average of 80-100 mm from late Monday to Tuesday, were the heaviest in three years, the weather bureau said.
Most major roads in Manila were inundated by knee- to waist-deep floodwaters. Some flights were delayed or cancelled. Power, water and communications in flooded areas were disrupted.
Some of the affected residents were marooned on the roofs of their houses.
"There are about 5,000 people here," said Ester Ronabio, a public school teacher and volunteer in one of the temporary shelter areas in low-lying Marikina City in the eastern part of Manila. "We can't control the flow of people."
In a sign of the difficult scramble to move people to safety, Aquino appealed to an anti-graft court to release dozens of rubber boats held as evidence in a case against senior police officials for use in evacuation efforts.
Residents of Manila expressed concern the rains were a repeat of Typhoon Ketsana which killed more than 700 people and destroyed $1 billion worth of private and public property.
"The floods are so deep where we live, we don't want a repeat of Typhoon Ketsana a few years ago," Melanio David, a father of four, told Reuters. "We got scared so we evacuated last night."
Asian Defence News