Armed men seized the regional government headquarters and parliament on Ukraine's Crimea peninsula on Thursday and raised the Russian flag.
A Reuters correspondent on the scene in the Crimean capital, Simferopol, said the door of the parliament was blockaded from inside by tables and chairs and no one was now able to enter.
Interfax news agency quoted a witness as saying there were about 60 people inside and that they had many weapons. It said no one had been hurt when the buildings were seized in the early hours of Thursday.
"I heard gunfire in the night, came down and saw lots of people going in. Some then left. I'm not sure how many are still in there," a 30-year-old man who gave his name only as Roman told Reuters.
Crimea, the only Ukrainian region with an ethnic Russian majority, is the last big bastion of opposition to the new political leadership in Kiev following the ouster of President Viktor Yanukovich on Saturday.
Ukraine's new leaders have been voicing alarm over signs of separatism there. The seizure of the building was confirmed by the country's acting interior minister, Ukrainian television said, but he gave few details.