“Gunshots have been heard, the bus is damaged,” Ukrainian President Volodymyr Zelensky said in a Facebook post, adding authorities are working to resolve the ongoing situation without casualties.
There have not yet been any reports of injuries or deaths.
A gunman armed with explosives has taken over a passenger bus with around 20 people on board in the western Ukrainian city of Lutsk, according to police.
Police said in a video statement posted on Facebook they did not yet have any information about possible casualties and “can only see mechanical damage to the bus.”
They are in touch with the hostage-taker and he says he has “explosives and arms” and “posted demands on Twitter”.
The man had given his name and police said they were checking if it was his real identity.
Authorities have also checked the Twitter account associated with the name but they had not found any demands “just general discontent about the system”.
Police added in the video they had tried to call the man back to find out his demands but he had not picked up. “We are going to conduct negotiations,” they added.
The centre of Lutsk has been sealed off to the public.
Police have opened a criminal investigation into the hostage-taking.
Ukraine’s Interior Minister Arsen Avakov is reportedly on his way to the Volyn region.