The presidential candidate of Poland's conservative opposition party has started his campaign, vowing to protect weaker social groups and to follow the policy of late President Lech Kaczynski who was killed in a 2010 plane crash.

Andrzej Duda, 42, of the Law and Justice party opened his campaign Saturday in a festive meeting with party leaders and backers. He vowed to lower the retirement age, and to care for the unemployed, miners and farmers, who are currently protesting the loss of jobs and falling prices for their produce.

Three other candidates have so far declared to run in the May 10 election: President Bronislaw Komorowski, who leads in the opinion polls; trans-gender lawmaker Anna Grodzka and left-wing Magdalena Ogorek, a young former TV presenter with almost no political experience.