Russian ships could not navigate the Amur River, and Russian troops were sent to Harbin. Blagoveshchensk was unprotected and, after hearing about the atrcoities committed against foreigners in China, on edge.
In retaliation and fear, City Police Chief Batarevich and the Military Governor Gribsky ordered that all the Chinese living in the city be rounded up and forced to cross the Amur. Estimates say between 4,000 and 8,000 Chinese died during that forced swim across the river. Many drowned, and those who would not leave the shore were killed with bayonet, sword or gun.
Aleksander Vasilievich Veresschagin, a colonel of the Russian General Staff, wrote an account of events based on his interactions and interviews with people who were in Blagoveshchensk at the time. He arrived in the city about 3 weeks after everything had occurred and did not experience it firsthand.
How does the Boxer Rebellion figure into the Treasure of Nikolai Nikolaevich: Adventures on the Amur #1?
Sources: https://en.wikipedia.org/wiki/Honghuzi
https://en.wikipedia.org/wiki/Blagoveshchensk
https://www.academia.edu/32724529/The_Blagoveshchensk_massacre_of_July_1900