To prevent Japanese advances in western and southern China, Chiang Kai-shek, at the suggestion of Chen Guofu, ordered the opening of the dikes on the Yellow River near Zhengzhou. The original plan was to destroy the dike in Zhaokou, but due to difficulties in that place, the Huayuankou dike on the south bank was destroyed on 5 June and 7 June by excavation, with flood waters over eastern Henan, central Anhui, and north central Jiangsu. The floods covered and destroyed thousands of square kilometers of agricultural land and displaced the mouth of the Yellow River hundreds of miles to the south. Thousands of villages were flooded or destroyed and several million villagers were forced to evacuate from their homes. 400,000 people including Japanese soldiers drowned and an additional 10 million became refugees. Rivers were filled with corpses as Tanka boat dwellers drowned from boat capsize. Damage to plantations also affected the population which generated later hunger. Despite this, the Japanese captured Wuhan on 27 October 1938, forcing the KMT to retreat to Chongqing (Chungking), but Chiang Kai-shek still refused to negotiate, saying he would only consider talks if Japan agreed to withdraw to the pre-1937 borders. In 1937, the Japanese Imperial Army quickly marched into the heart of Chinese territory.