City officials said that 76 million yen ($950,000) has been contributed since a special account for donations was set up last Friday, Kyodo News reported.
The Senkaku Islands include five islands and three rocks, all uninhabited. They are about equally distant from Japan and China, and somewhat closer to Taiwan.
Japan annexed the islands more than a century ago, but both China and Taiwan say they are part of Taiwan, which in China's eyes would make them Chinese territory. China calls them the Diaoyu islands and to the Taiwanese they are the Diaoyutai.
Tokyo Gov. Shintato Ishihara said last month the city is negotiating to buy three of the islands.
Japanese entrepreneur Koga Tatsushiro built a bonito processing plant on the islands in the early 1900s. Though the business failed in the early 1940s, the plots of land are technically the private property of his descendants, the Kurihara family, who live in Saitama prefecture.