The Ministry of Emergency Management has dispatched 1,800 firefighters from nearby regions to support disaster relief work in Henan province after historically rare torrential rains prompted the evacuation of local residents.

With expertise in water rescue, the group has rushed to the region in Central China with 250 speed boats and over 18,500 sets of other equipment for flood control and emergency rescue, a media release from the ministry said.

The firefighters are from seven provincial regions, including Hebei, Shanxi, Jiangsu and Anhui provinces, it added.

In Henan, the provincial fire service headquarters had on Tuesday mobilized 180 firefighters from six cities to join the rescue efforts in Zhengzhou, the province's capital and worst-hit area in a rain the local meteorological authority said "happens only once in a millennium".

As of 5 am on Wednesday, the provincial fire service headquarters had rescued 5,574 people trapped by floods and also relocated 11,397 people to safe areas, it said.

The amount of precipitation falling from 8 pm Saturday to 8 pm Tuesday in Zhengzhou had reached 617.1 millimeters, compared with the annual average of 640.8 mm.