"The duration, scope and impact of the drought are rare," state media quoted Zheng Guoguang, chief of the China Meteorological Administration, as saying on Thursday.
Weather officials in the central province of Henan, one of China's most populous with 93.6 million people, said 105 days without rain makes it the worst drought since 1951.
China's Office of State Flood Control and Drought Relief has declared a "level 2" emergency, calling it a "severe drought rarely seen in history", the People's Daily reported.
|The dry spell is expected to affect 40 per cent of China's wheat production [Reuters]
On Wednesday Chinese agriculture officials tried to ease worries about lost crops saying that almost 40 per cent of the major drought-hit areas including Henan, Shandong and Hebei, had been irrigated.
Local officials have been asked to make drought-relief work their top priority.
Zhang Zhitong, a deputy chief of the office, said local officials must make "fighting the drought and protecting seedlings a major task" and expand irrigation coverage.
In the capital Beijing further north it more than 100 days have passed without rain, a situation not seen in 38 years, the China Daily said.
Some analysts say the drought could reduce annual production in major wheat-growing areas by between two and five per cent.
"The severest-hit regions of Henan and Anhui will see their wheat harvest down by about 20 per cent," Ma Wenfeng, an analyst, told the China Daily.