Pro-Russian forces stormed a Ukrainian air force base in Crimea, firing shots and smashing through concrete walls with armoured personnel carriers.
An APC also smashed open the front gate of the Belbek base near the port city of Sevastopol, according to footage provided by the Ukrainian Defence ministry.
The Ukrainian commander of the base, Yuliy Mamchur, said there was at least one injury. He called his men together, they sang the Ukrainian national anthem and then stood at ease. He said they were going to turn over their weapons.
Elsewhere, more than 5,000 pro-Russia residents of a major city in Ukraine's east demonstrated in favour of holding a referendum on whether to seek to split off and become part of Russia.
The rally in Donetsk came less than a week after the Ukrainian region of Crimea approved secession in a referendum regarded as illegitimate by Western countries. After the referendum, Russia formally annexed Crimea.
With Crimea now effectively under the control of Russian forces, which ring Ukrainian military bases on the strategic Black Sea peninsula, concern is rising that Ukraine's eastern regions will agitate for a similar move.
Russia has brought large military contingents to areas near the border with eastern Ukraine. Russian President Vladimir Putin has said there is no intention to move into eastern Ukraine, but the prospect of violence between pro- and anti-secession groups in the east could be used as a pretext for sending in troops.
Eastern Ukraine is the heartland of Ukraine's economically vital heavy industry and mining.
It's also the support base for Viktor Yanukovych, the Ukrainian president who fled to Russia last month after three months of protests in the capital, Kiev, triggered by his decision not to sign an agreement with the European Union.
Russia and Yanukovych supporters contend Yanukovych's ousting was a coup and allege the authorities who then came to power are nationalists who would oppress the east's large ethnic Russian population.
"They're trying to tear us away from Russia," said 59-year-old demonstrator Igor Shapoval.
As tensions roil in the east, the Organisation for Security and Co-operation in Europe is deploying a 200-strong observer team aimed at easing the crisis.
It is unclear whether the team will be allowed into Crimea.
The seizure of military facilities and navy ships by pro-Russian forces in Crimea has been proceeding apace since the peninsula was nominally absorbed by Russia.
Yesterday, a crowd stormed the Novofedorivka base, 50 kilometres west of Simferopol, Ukraine's Defence Ministry said.
Ukrainian television station TSN said troops inside the base hoisted smoke grenades in an attempt to disperse groups of burly young men attempting to break through the front gates.