"Since February 24, a total of 6,141,000 people have crossed into Poland from Ukraine," it said in a tweet.
On Thursday, some 23,400 refugees from Ukraine arrived in the country, compared with around 21,600 a day earlier, according to the Polish Border Guard.
Meanwhile, over 4.35 million people have left Poland for Ukraine since February 24, the agency also reported.
On Thursday, some 21,800 people crossed from Poland into Ukraine, the Polish Border Guard said.
A deputy interior minister said in mid-June that Poland was home to some 1.5 million Ukrainians after many refugees from Russia's invasion of Ukraine decided to return to their country.
Poland in March enacted a measure to offer wide-ranging support to Ukrainians escaping the Russian invasion of their country, which began on February 24.
The measure grants them residence rights and ensures access to education, healthcare and social benefits.
Eighty-four percent of Poles are in favour of accepting refugees from war-torn Ukraine, according to a survey.