The Bắc Lệ ambush (French: guet-apens de Bac-Lé, Vietnamese: trận Bắc Lệ or trận cầu Quan Âm) was a clash during the Tonkin Campaign in June 1884 between Chinese troops of the Guangxi Army and a French column sent to occupy Lạng Sơn and other towns near the Chinese border.

The defeat at Bắc Ninh, coming close on the heels of the fall of Sơn Tây, strengthened the hand of the moderate element in the Chinese government and temporarily discredited the extremist 'Purist' party led by Zhang Zhidong, which was agitating for a full-scale war against France.

In fact, the Chinese stance was an ex post facto rationalisation, designed to justify their unwillingness or inability to put the terms of the accord into effect.

The war party called for Li Hongzhang's impeachment, and his political opponents intrigued to have orders sent to the Chinese troops in Tonkin to hold their positions.

In early June 1884 a French column under the command of Lieutenant-Colonel Alphonse Dugenne advanced to occupy the border towns of Lạng Sơn, Cao Bằng and That Khe.

As the French were advancing through unknown country, Captain Jean-François-Alphonse Lecomte of the topographical service rode with the column to map the route.

The march, under a sweltering summer sun, was gruelling, and on 15 June Dugenne sent Jourdy's battery back to Phu Lang Thuong.

For the next three days the column pressed on to the northeast, marching parallel to the course of the Thuong river and camping in the open country between Cau Son and the small town of Bắc Lệ.

Believing that he was dealing with stragglers from the Guangxi Army who would not oppose his passage, Dugenne gave orders for a crossing of the Song Thuong the following morning.

Both commanders were aware of the provisions of the Tientsin Accord, but as a result of the political intrigues aimed at Li Hongzhang they had received no instructions to withdraw from Tonkin.

[8][9] At dawn on 23 June Captain Lecomte crossed the Song Thuong with the column's advance guard (two companies of French infantry, a section of Tonkinese riflemen and a small party of cavalry).

According to Captain Lecomte (normally a reliable source), Dugenne believed that the Chinese would let him pass, and his intention was merely to get his column away from the swollen Song Thuong River and to find a secure camping ground for the night.

For several minutes the French column marched unmolested along a jungle path towards a group of Chinese forts on the cliffs of Nui Đồng Nai.

Seeing the path opening into a clearing, Dugenne ordered Laperrine's cavalry to replace an inexperienced section of Tonkinese riflemen at the front of the column.

As the French cavalry spurred their horses forward to move to the front of the column, Chinese infantry in the Nui Đồng Nai forts suddenly opened fire on them.

However, the Chinese brought up fresh troops during the night, and occupied positions on the heights of Nui Đồng Nai from which they could fire down on the French square.

[15] On the morning of June 24, the Chinese worked their way around the sides of the French square in an attempt to cut the column's line of retreat to the Song Thuong.

Dugenne made several local counterattacks to take some air around his positions, but it soon became obvious that, with no artillery support, the French would be encircled and annihilated if they remained where they were.

In the afternoon of 24 June the column retreated to Bắc Lệ, followed at a respectful distance by the victorious Chinese, and occupied a defensive position on a high plateau.

[Note 2] Travelling upriver aboard a flotilla of steamboats to Phu Lang Thuong and thereafter marching light, de Négrier's relief column reached Cau Son on the evening of 25 June.

[20] De Négrier joined Dugenne's column near Bắc Lệ on the morning of 27 June and made preparations for an immediate counterattack to throw the Chinese back across the Song Thuong.

During the night of 28 June, under cover of a heavy thunderstorm, he and Dugenne withdrew their respective commands from the Bắc Lệ plateau unnoticed by the Chinese.

On the afternoon of 29 June the French reached Cau Son, where the wounded from the Bắc Lệ battle were evacuated back to Phu Lang Thuong by junk.

The mood in France was against compromise, and although negotiations continued throughout July, Admiral Amédée Courbet was ordered to take his Far East Squadron to Fuzhou (Foochow).

The negotiations broke down in mid-August and on 23 August 1884, at the Battle of Fuzhou, Courbet annihilated China's Fujian Fleet, inaugurating the nine-month Sino-French War.