BEIJING: Typhoon Muifa gained strength in the East China Sea on Wednesday, triggering China's first "red alert" this year, forcing flight and train cancellations in Shanghai and threatening the busy port shared by Ningbo and Zhoushan cities.

More than 50% of flights were reduced or cancelled at Shanghai's Pudong and Hongqiao airports with 589 flights already affected, while the city of Hangzhou, to the southwest of Shanghai, will cancel domestic flights from the evening, according to state media.

Flights at Zhoushan and Ningbo airports, in the coastal province of Zhejiang, were also cancelled, while the bunkering hub shared by both cities temporarily suspended discharging and loading oil, and ordered tankers to stay at anchorages. 

Shanghai, which earlier issued an advisory warning wind gusts and heavy rains were expected until Thursday, took safety measures a step further by announcing plans to limit speeds for ground elevated trains or even close stations, and warned of train delays to ensure safety in affected areas while keeping other sections operating.

Muifa is expected to move northwest at a speed of 20-25 kmh (12-15 mph) and expected to make landfall along coastal cities in Zhejiang province on Wednesday evening, then pass through Hangzhou Bay to make a second landfall in Shanghai, according to forecasters.

Chinese financial magazine Caixin reported that Muifa was the strongest typhoon in the Yangtze River Delta in a decade, which meteorologists said was caused by this year's unusually hot weather and high temperatures in the East China Sea.

Zhejiang authorities issued a "red warning" for flash floods in several areas and the national weather forecaster said there was a high risk of flooding of small and medium-sized rivers in northeast Zhejiang and waterlogging in eastern and northern Zhejiang, Shanghai, southern areas of Jiangsu province and other places.