While the NRA Second Collective Army advanced northeast to Jinan along the southern bank of the Yellow River, the First Collective Army diverged east from the Tianjin–Pukou railway at Tai'an, crossing the Taishan mountains to attack Jinan from the west via the Qingdao–Jinan railway. This strategy was successful, and by 29 April, the NRA had nearly encircled Jinan. The beleaguered NPA retreated to the north bank of the Yellow River, amidst looting and outbreaks of violence. At this point, there were already 3,000 Japanese troops in Jinan, guarding the 2,000 Japanese civilians in the city. On the next day, NRA troops entered Jinan. Chiang Kai-shek arrived on 2 May, and attempted to negotiate a Japanese withdrawal from Jinan, issuing safety guarantees for Japanese civilians to local Kwantung Army commander Hikosuke Fukuda. Fukuda agreed, and his troops prepared to leave that night. Early the next morning, conflict broke out between the Chinese and Japanese troops, starting what came to be called the "Jinan incident". What began as a minor armed altercation escalated on 8 May into a full-scale Japanese attack on the city. During the course of the incident, the Japanese killed KMT foreign affairs commissioner Cai Gongshi, several diplomats, and about five thousand Chinese civilians.