According to the head of the Lithuanian Border Guard Rustam Lyubaev, different sources claim there are 10 000 to 50 000 illegal migrants currently staying on the Belarusian-Polish border. According to him, the news about migrants concentrating along the border were received at the end of last week, stressing that the Lithuanian border guard are preparing for possible developments.

I am not sure if the given numbers are accurate, but I think there is no way to know it.