German Chancellor Angela Merkel's conservatives widened their lead in the latest Ipsos poll over the Social Democrats (SPD), as the centre-left party's gains of recent weeks began to ease.

The Ipsos poll put the conservative bloc at 33 percent, while the SPD, which had seen a surge in support after it nominated former European Parliament President Martin Schulz as its candidate to replace Merkel, was at 29 percent.

"The Schulz effect is clearly wearing off," wrote the pollsters.

The poll said there was a one percentage point gain for both the Free Democratic Party, which rose to 6 percent, and the pro-environmental Green party, which rose to 8 percent. The anti-immigrant lost one percentage point to 11 percent.

The poll surveyed 1,058 people in Germany from March 3-6.