BEIJING, Sep 14 (Reuters) - Typhoon Muifa gained strength in the East China Sea on Wednesday (Sep 14), forcing the cancellation of hundreds of flights out of the financial hub of Shanghai and threatening the busy port shared by Ningbo and Zhoushan cities.

Zhejiang province upgraded its typhoon emergency response to the highest level as Muifa is expected to move northwest at a speed of 20kmh to 25kmh, intensifying and eventually reaching coastal areas south of Zhoushan, according to the China Meteorological Administration.

China's 12th cyclone of the year was expected to make landfall on Wednesday afternoon or night, according to forecasters. Shanghai issued an advisory warning for wind gusts and heavy rains are expected until Thursday.

More than 50 per cent of flights will be reduced or cancelled at Shanghai Pudong Airport and Hongqiao Airport on Wednesday with 589 flights already affected, according to state media.

Flights at Zhoushan and Ningbo airports were also cancelled.

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 and other places.