Dense fog affected Shanghai yesterday, blocking dozens of ships and ferry boats and delaying at least 150 flights.

Shanghai Wusong Port said visibility in the morning fell to less than 1,000 meters in port areas, shrinking as little as 200 meters in some places - lower than the minimum sailing standard.

At least 400 ships changed their sailing schedules and the 180 commuter ferries for Chongming Island and on the Huangpu River in the city's suburban areas stopped running in the morning, said the Shanghai Maritime Safety Administration.

Shanghai Meteorological Bureau said similarly heavy fog should affect the city again this morning. The bureau said to expect high humidity, weak winds and visibility of just 500 to 1,000 meters.

The bureau issued a yellow fog alert, lowest of the three-leveled system, at 4:40am. Although the alert was lifted at 8:35am with the mist starting to dissipate, the situation in the Wusong port remained difficult, with visibility still under 1,000 meters at the mouth of the Yangtze River. The ships, including 64 international ones, were still waiting to enter and exit the port, officials said.

Rainy weather should continue today and tomorrow, the weather bureau said.