German conservative leader Friedrich Merz is set to take his hard-line immigration push to the next level despite a growing backlash over his move this week to force a resolution through parliament with backing from the far right.

Germany's opposition conservatives won parliamentary approval on Wednesday for a proposal to drastically restrict migration with the help of votes from the Alternative for Germany (AfD), breaking a taboo on cooperation with the far-right.

The German parliament is debating motions to tighten migration rules after a deadly attack by a rejected asylum seeker. CDU leader Friedrich Merz says he will not shun the help of the far-right AfD to push them through.

German lawmakers are set to vote on Wednesday on two motions tabled by the centre-right opposition bloc to significantly tighten the country's migration policy, less than four weeks before Germans head to the polls in national elections.