For several days now, 3,000 more Ukrainians on average have entered Poland than have left, according to the Polish border authorities.
On Thursday, 27,500 people from Ukraine entered Poland while 24,400 crossed the border in the opposite direction, the border guard said.
On Wednesday, there were 26,300 Ukrainian arrivals and 23,500 departures.
The Ukrainian border guard also noticed the change.
It said 45,000 people left Ukraine via its Western borders on Thursday, including more than 25,000 who crossed into Poland. A further 40,000 entered Ukraine, including 37,000 Ukrainian citizens.
The change comes amid Russia's continued bombing of Ukrainian cities and the destruction of infrastructure, including the Kremenchuk oil refinery, that has left thousands without jobs, according to Natalia Panchenko, head of the Euromajdan Warszawa citizens' initiative in support of Ukraine.
"Over time, even the greatest holdouts can lose their nerve," she told AFP
Panchenko said she did not know the exact reason for the recent uptick in arrivals.
After Russia invaded Ukraine on February 24, Ukrainians fled in droves to Poland, a European Union country. Sometimes as many as 140,000 arrived per day, border guard spokeswoman Anna Michalska said.
Michalska told AFP she did not think the change was large enough to be significant. Only nine percent of Ukrainians crossing into Poland say they are fleeing the war at home, she added.