The Alternative for Germany party campaigned hard against her stance on refugees
An anti-immigration, nationalist group has beaten Angela Merkel's party in a state election in Germany, exit polls suggest.
The Alternative for Germany party (AfD), which has campaigned hard against Chancellor Merkel's policies on refugees, is estimated to have won 21% in the Mecklenburg-Vorpommern contest.
It could amount to a stinging defeat for Mrs Merkel's Christian Democrats, who are projected to gain 19% or 20% of the vote, putting them in third place.
Although the centre-left Social Democrats are expected to retain first place, they are projected to win 30.5% of the votes - a fall of five percentage points compared to 2011.
The deputy leader of the AfD, Beatrix von Storch, told Sky News that the exit poll result would be a "huge success" for her party, which was only founded three years ago.
"This is what we call probably the beginning of the end of Angela Merkel's chancellorship," Ms von Storch added. Mecklenburg-Vorpommern, a small coastal state in northeastern Germany, only has 1.3 million eligible voters.
However, the area is particularly significant for Mrs Merkel as it is home to her own electoral district. The German leader's open-door refugee policy was a key issue in Sunday's state election.
Mrs von Storch told Sky News that Mrs Merkel's approach to refugees is "going to destroy Germany and Europe", adding: "We have to protect our borders. People do not support this policy anymore."
Back in March, voters in three other states rejected the Christian Democrats and voted in increasing numbers for the AfD - a trend which could prove problematic for the Chancellor, who may run for a fourth term.