On 15 January 1857, during the Second Opium War, several hundred European residents were poisoned non-lethally by arsenic, found in bread produced by a Chinese-owned store, the Esing Bakery.

The true responsibility for the incident and its intention—whether it was an individual act of terrorism, commercial sabotage, a war crime orchestrated by the Qing government, or purely accidental—both remain matters of debate.

The scale and potential consequences of the poisoning make it an unprecedented event in the history of the British Empire, the colonists believing at the time that its success could have wiped out their community.

In 1841, in the midst of the First Opium War, Captain Charles Elliot negotiated the cession of Hong Kong by the Qing dynasty of China to the British Empire in the Convention of Chuenpi.

[9] At the opening of the war in late 1856, Qing imperial commissioner Ye Mingchen unleashed a campaign of terrorism in Hong Kong by a series of proclamations offering rewards for the deaths of what he called the French and British "rebel barbarians", and ordering Chinese to renounce employment by the "foreign dogs".

[11] At the same time, Europeans in Hong Kong became concerned that the turmoil in China caused by the Taiping Rebellion (1850–1864) was producing a surge of Chinese criminals into the colony.

[15] The colony's doctors, led by Surgeon General Aurelius Harland, dispatched messages across the town advising that the bread was poisoned and containing instructions to induce vomiting and consume raw eggs.

[17] The proprietor of the bakery, Cheong Ah-lum (Chinese: 張霈霖; Jyutping: zoeng1 pui3 lam4; Cantonese Yale: Jēung Puilàhm[13]), left for Macau with his family early in the day.

Governor Bowring and his Executive Council had determined while the trial was still underway that Cheong should be detained indefinitely regardless of its outcome,[29] and he was arrested soon afterwards under emergency legislation on the pretext of being what the authorities called a "suspicious character".

[30][n 4] Before the sentence could be executed, Bridges, now Acting Colonial Secretary, accepted a petition from the Chinese community for Cheong to be allowed to leave peaceably from Hong Kong after putting his affairs in order.

The historian George Beer Endacott argued that the poisoning was carried out on the instruction of Qing officials, while Jan Morris depicts Cheong as a lone wolf acting out of personal patriotism.

Cheong's own clan record, written in China in 1904 at the command of the imperial court, states that the incident was entirely accidental, the result of negligence in preparing the bread rather than intentional poisoning.

[17] In June 1857, the Hong Kong Government Gazette published a confiscated letter written to Chan Kwei-tsih, the head of the resistance committee in Xin'an County, from his brother Tsz-tin, informing him of the incident.

[34][n 5]Portions of the poisoned bread were subsequently sealed and dispatched to Europe, where they were examined by the chemists Frederick Abel[15] and Justus von Liebig, and the Scottish surgeon John Ivor Murray.

[35] News of the incident reached Britain during the 1857 general election,[36] which had been called following a successful parliamentary vote of censure of Lord Palmerston's support for the Second Opium War.

[39] In London, the incident came to the attention of the German author Friedrich Engels, who wrote to the New York Herald Tribune on 22 May 1857, saying that the Chinese now "poison the bread of the European community at Hong Kong by wholesale, and with the coolest premeditation".

[43] Both the scale of the poisoning and its potential consequences make the Esing bakery incident unprecedented in the history of the British Empire,[44] with the colonists believing at the time that its success could have destroyed their community.

[18] Morris describes the incident as "a dramatic realization of that favourite Victorian chiller, the Yellow Peril",[45] and the affair contributed to the tensions between the European and Chinese communities in Hong Kong.

[22] Soon after the poisoning, Hong Kong was rocked by the Caldwell affair, a series of scandals and controversies involving Bridges, Tarrant, Anstey, and other members of the administration, similarly focused on race relations in the colony.