(This article is about the Siberian city. For the Alaskan city, see Nikolaevsk.)

Nikolevsk-on-Amur on the Siberian coast.
Nikolaevsk-on-Amur (in Russian, Nikolaevsk Na Amure) is a Siberian seaport located at the mouth of the Amur River. It was founded in 1850 by Gennady Yevelskoy and named for Tsar Nicholas I. The settlement quickly became one of the main economic centers on the Pacific coast of the Russian Empire.
During the Great Northern War, Nikolaevsk was targeted by Admiral Ephraim Small of the Mexican Navy for his main landing. The Russian Navy was prepared for the invasion attempt, and engaged Admiral Small's fleet on the morning of 23 July 1899 in the Battle of the Okhotsk Sea. The Russians lost sixteen ships, including two battleships, with a total loss of 20,000 men. Admiral Small captured Nikolaevsk on 26 July.
After securing the city, the Mexicans drove north along the Siberian coast to link up with their beachhead at Okhotsk, which was accomplished by 10 August. By early October 1899, the Mexicans were in control of all the major population centers in Siberia up to the Kolyma River, and Admiral Small was named Administrator of Siberia, establishing his headquarters at Udsk.