During the spring of 1884 the Tonkin Expeditionary Corps, under the command of General Charles-Théodore Millot, routed China's Guangxi Army in the Bắc Ninh campaign (February 1884) and completed the French conquest of the Red River Delta by capturing Hưng Hóa (March 1884), Thái Nguyên (May 1884) and Tuyên Quang (June 1884).

In late September 1884 large detachments of the Guangxi Army advanced from Langson and probed into the Luc Nam valley, announcing their presence by ambushing two French gunboats of the Tonkin Flotilla, Hache and Massue, on 2 October.

Although French casualties during this ambush were relatively high (1 officer killed and 32 men wounded), the attack deprived the Chinese of strategic surprise.

The first column, under the command of Lieutenant-Colonel Donnier, included two companies of the 143rd Line Battalion (Captains Cuvellier and Fraissynaud), two companies of chef de bataillon Diguet's 2nd Foreign Legion Battalion (Captains Beynet and Bolgert), 50 Tonkinese riflemen (2nd Lieutenant Bataille) and a section of de Saxcé's artillery battery.

The Guangxi Army was under the command of generals Wang Debang and Pan Dingxin, both of whom had contributed to the defeat of Lieutenant-Colonel Dugenne's column in June 1884 in the Bắc Lệ ambush.

[5] De Négrier planned to use the mobility conferred by the French gunboats to manoeuvre troops rapidly from one point to another, enabling him to concentrate in turn against the separated wings of the Guangxi Army.

In the event, Donnier won his battle, and on 13 October de Négrier joined him with the Kép column and began to scout the Guangxi Army's defences around Chu in preparation for an assault by the united French forces.

The battle was marked by bitter close-quarter fighting between French and Chinese troops, and de Négrier's soldiers suffered heavy casualties storming the fortified village of Kép.

The exasperated victors shot or bayoneted scores of wounded Chinese soldiers after the battle, and reports of French atrocities at Kép shocked public opinion in Europe.

[7] At Chu, on 10 October, a morning outpost skirmish precipitated by an over-zealous Foreign Legion officer, Captain Cuvellier, escalated into a full-scale afternoon battle in which Donnier's bridgehead at Tray Dam was violently attacked by the Chinese.

Concentrated, aimed French volleys inflicted heavy casualties on the dense Chinese attack columns and eventually put them to flight.

[8] In the wake of these French victories the Chinese fell back to Bắc Lệ and Dong Song, while de Négrier established important forward positions at Kép and Chu, which threatened the Guangxi Army's base at Lạng Sơn.