SHANGHAI - Heavy fog on Tuesday delayed flights and ships in China's commercial hub Shanghai, and also caused deadly road accidents in the city and other parts of the country.

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More than 30 incoming flights destined for Shanghai Pudong International Airport landed at Shanghai Hongqiao International Airport between 8 pm Monday and 8 am Tuesday.

Heavy fog has covered the city since late Monday, reducing visibility to less than 100 meters Tuesday morning, said the Pudong airport spokesman.

An emergency response plan had been activated by the airport to cope with an influx of flights when the skies cleared, said the spokesman.

Maritime authorities in Shanghai also started an emergency response plan to ensure ships could sail smoothly in and out of the city's ports when the fog lifted.

Some international ships delayed or canceled sailing plans after the Shanghai Meteorological Center issued a heavy fog warning at 22:50 pm Monday.

By 1:40 pm Tuesday, more than 100 ships from two ports, Waigaoqiao port in Pudong and Yangshan deep water port in Hangzhou Bay, had canceled sailing plans, said the Shanghai ports spokesman.

Fog was expected to sweep most parts of China on Tuesday, with visibility reduced to less than 200 meters in parts of Beijing and Tianjin, said a warning issued by the National Meteorological Center Monday night.

Tuesday's fog also caused a pile-up that killed three and injured an unknown number of passengers on a cross-sea bridge in Shanghai.

The accident, involving more than 10 vehicles, happened at about 7 am on the East China Sea Bridge, which links Shanghai with Yangshan Isle in Hangzhou Bay.

Also, three people died in two pile-ups noon Tuesday in the Huangguoshu section of the Hu-Kun Expressway that links Shanghai with Kunming, capital city of Southwest China's Yunnan province.

The first pile-up involved eight vehicles amid fog and rain and the second involved over 20, a spokesman with the traffic police in Guizhou province said.

Police are still striving to rescue two people from the damaged vehicles, the spokesman said.