The second loss in two weeks for the Christian Democrats has triggered calls from CSU allies to toughen up the migrant policy
German Chancellor Angela Merkel's Christian Democrats party suffered a heavy setback on Sunday, its second electoral blow in two weeks.
The CDU slumped to its lowest level since 1990 in a Berlin state vote that rejected her open-door refugee policy.
Merkel's party won just 18 per cent which will likely spell the end of its term as a junior coalition partner to the Social Democrats (SPD), who won almost 22 percent.
Merkel's decision to open Germany's borders to refugees a year ago boosted support for the anti-immigrant Alternative for Germany (AfD) party. There have been concerns about the cost of letting the migrants in and their integration.
Voters turned to AfD that garnered 12.9 percent of the vote and won 10 of the 16 seats.
"From zero to double digits, that's unique for Berlin. The grand coalition has been voted out - not yet at the national level, but that will happen next year," said AfD candidate Georg Pazderski to cheering supporters after the results.
Commentators said the result indicated that the party looked poised to enter the lower house of parliament in 2017.
"With the Berlin result, the AfD has consolidated its position and shown it can appeal to voters across the board - it is now represented in a big city, eastern German states and in more affluent western states like Baden-Wuerttemberg," said Thomas Jaeger, a political scientist at Cologne University.
A year before the national election, the result will bolster the chances for AfD and raise pressure on Merkel's party.
The rift within the conservative camp is only expected to deepen with these results. The CSU's Bavarian finance minister Markus Soeder said this should be viewed as the second massive wake-up call for the allies in Bavaria.
"A long-term and massive loss in trust among traditional voters threatens the conservative bloc," Soeder said.
He added that major changes to the coalition's immigration policy were required to win back supporters.
The losses for the biggest parties in Germany raise the possibility of different coalitions in future.
It also cast doubt over whether Europe's most powerful leader, Angela Merkel will stand for a fourth term next year.
Given a dearth of options in her party, however, she is still the most likely candidate.
(WION with inputs from agencies)