Thousands of backers of Poland's ruling conservative party are marching in Warsaw with the party leader to show their support for its policy amid a growing political conflict.

The march, led by Law and Justice party head Jaroslaw Kaczynski, comes a day after tens of thousands of government opponents demonstrated in Warsaw and elsewhere, saying the ruling party and President Andrzej Duda are threatening democracy.

The ruling party and the opposition are in conflict over the appointment of new judges to the Constitutional Tribunal, the top law arbiter.

Opening the march Kaczynski said Law and Justice, in power since last month, is aiming for a wide reform of Poland, but the opposition is preventing that.