Turkish citizens in six European countries have started to vote in a referendum, the campaign for which has caused an international dispute.
Some three million people are eligible to vote outside of Turkey, almost half of them living in Germany.
But political rallies have been blocked in several countries.
This has caused a bitter row between Turkey and its European neighbours, with President Erdogan accusing the Dutch and German authorities of acting like Nazis.
In Switzerland, a rally in support of the "no" vote was held in Bern on Sunday, drawing thousands - including Kurdish demonstrators.
Read m,ore: Voting starts in Europe for Turkish referendum - BBC N