Authorities should send emergency teams to drain water from fields, speed up access by harvesters and mobilise drying machinery to save as much of the crop as possible, said the ministry late on Tuesday.

Giving further advise to these authorities, the ministry said: "Make full use of various places such as town squares or playgrounds, the front and back of houses to dry and harvest wheat to prevent sprouting and mould."

China, the world's top wheat grower, had expected a bumper crop this year. But heavy rain across the southern half of central Henan province last week is raising concerns.

Henan produced 28% of China's crop of 137 million tonnes in 2021.

Darin Friedrichs, co-founder of Shanghai-based Sitonia Consulting said it was too early to say how much output would be affected, but "the harvest is definitely going to be impacted."

"The harvest was just ramping up and some areas have seen 400% precipitation anomalies over the past 10 days," he added.

Some wheat in southern Henan has sprouted after the rain, the government-backed Henan Daily said on Wednesday, making it unfit for consumption.

More than 90% of the wheat around the city of Nanyang has sprouted, said a local harvester, referring to a county in the south of the province, while Zhumadian county is also impacted.

Buyers are purchasing the sprouted wheat at around 1,000 yuan ($144.67)to 1,200 yuan per tonne, half of the normal price, he said, declining to be identified because of the sensitivity of the topic.

The spot wheat price in Zhengzhou fell 1.5% to 2,700 yuan on Monday, weighed down by lower quality supply.

Sprouted wheat is also being seen in northern Shandong province, said the state-backed media Cngrain.com.

The agriculture ministry urged buyers to purchase sprouted wheat that can still be used for feed or industrial purposes, while making sure it does not go to food.

The rain is also leading to blight in some areas, videos posted on social media and a local grain dealer said this week.

($1 = 6.9121 yuan)