Poland's conservative ruling party is facing its first test of support since it took power in November as by-elections to the Senate are being held in country's northeast.

The vote is being held in the Lomza and Augustow region because its senator vacated his seat when he was recently appointed provincial governor. Among the six candidates is Anna Maria Anders who represents the ruling Law and Justice party.

Party leader Jaroslaw Kaczynski has said the vote is a test of support for the party that is introducing sweeping changes to state offices and to social benefits.

Recent appointments to the Constitutional Court and to top positions in state media have led to massive street protests and censure from European Union leaders.