Warsaw's liberal mayor Rafal Trzaskowski won a narrow victory in Poland's presidential election, but a second-round run-off with conservative historian Karol Nawrocki will be required to decide the country's next president.

The mayor of Warsaw was poised for a narrow win over a pro-Donald Trump nationalist in the first round of Poland’s presidential election that is critical for the pro-European government’s agenda to undo years of populist rule.

Pro-EU Warsaw mayor Rafal Trzaskowski was set to face nationalist historian Karol Nawrocki in Poland's presidential runoff on June 1, an exit poll showed after the first round, as the far-right made record advances.