Support for German Chancellor Angela Merkel's conservatives has slipped to a one-year low of 38.5 percent, hit by voters' concerns about Europe's refugee crisis, a poll showed on Tuesday.

Merkel has drawn criticism, especially among conservatives, for fuelling the influx by effectively giving asylum seekers the green light to come to Germany. Towns and cities in Europe's biggest economy are struggling to cope with 800,000 refugees and migrants escaping war and poverty expected this year.

The INSA poll, conducted for Bild daily, showed a one percentage point decline for the conservatives from a week ago. The Social Democrats (SPD), who share power with Merkel in a right-left coalition, were also down one point at 23.5 percent.

That takes overall support for the "grand coalition" to its lowest level since the last election two years ago.

"The refugee crisis is causing problems above all for the conservative camp and the grand coalition is weaker than ever," INSA chief Hermann Binkert told Bild daily.

The radical Left party gained half a point to 10.5 percent, the same level as the Greens who were up 1 point. The right-wing Alternative for Germany (AfD) and pro-business Free Democrats (FDP) were both unchanged at 6 percent and 4 percent respectively.

Merkel's own popularity has also taken a hit over her handling of the refugee crisis although she is still one of Germany's most popular post-war chancellors.

The next election is due in 2017.