Poland reopened its borders with Germany, Czech Republic and Slovakia on Saturday, while the frontier with Lithuania had already been opened on Friday.
ADVERTISEMENTPoland has reopened all its EU borders for the first time in nearly three months.
The European Commission has recommended all borders in the bloc should open by Monday.
At the border with Germany the mayors of two neighbouring cities - Frankfurt on the Oder river on one side, and Slubice on the other - celebrated with champagne.
René Wilke and Mariusz Olejniczak were later seen breaking the existing coronavirus regulations by shaking hands.
"I am just realizing that something happened that was unimaginable," Wilke said.
When the border was closed in mid-March, commuters were prevented from working, but later an exception was made for them.
Poland's border with Lithuania was already opened on Friday. The Czech and Slovak borders had to wait until Saturday.
But the non-EU borders with Ukraine, Belarus and the Russian exclave Kaliningrad are still closed.
Workers and visitors from those countries face 14 days of quarantine once they arrive in Poland.
From Tuesday flights will also operate to EU destinations.