Russia has said China is largely "in agreement" over Ukraine, after other world powers condemned Moscow for sending troops into the country.
Hundreds of Russian soldiers have surrounded a military base in Crimea, preventing Ukrainian soldiers from going in or out.
The convoy blockading the site, near the Crimean capital Simferopol, includes at least 17 military vehicles.
Russian troops are also reported to have taken control of a ferry terminal in the city of Kerch on the eastern tip of Crimea, which has a majority Russian-speaking population.
Ukraine's defence ministry said two Russian fighter jets violated the country's air space in the Black Sea on Sunday night and that it had scrambled an interceptor aircraft to prevent the "provocative actions".
And reports claimed pro-Russian protesters had occupied a floor of the regional government building in Donetsk. The 11-storey building has been flying the Russian flag for the last three days.