Turkey should seek a broad national consensus on constitutional amendments, given the narrow majority supporting them and the extent of their impact, the European Commission said.

Unofficial results showed that 51.3 percent of Turks approved changes to their constitution in Sunday's referendum, handing President Tayyip Erdogan sweeping new powers.

"In view of the close referendum result and the far-reaching implications of the constitutional amendments, we also call on the Turkish authorities to seek the broadest possible national consensus in their implementation," the Commission said in a statement.

Turkey, a NATO member state that began talks to join the EU in 2005, has become a crucial partner for the bloc by taking in millions of refugees fleeing from the six-year-old war in Syria.

But a crackdown by Erdogan since a failed coup last July has been condemned in European capitals.

The European Union statement, issued by Commission President Jean-Claude Juncker and two other top officials, said the EU executive took note of the result and was awaiting an assessment of an international observation mission "also with regard to alleged irregularities".

The constitutional amendments would be assessed in the light of Turkey's obligations as a European Union candidate country, and as a member of the Council of Europe, which overseas democracy, human rights and the rule of law across the continent.

"We encourage Turkey to address the Council of Europe's concerns and recommendations, including with regards to the state of emergency," the Commission said.

Members of the European Parliament largely lamented the referendum result. Manfred Weber‏, leader of the centre-right grouping, said Erdogan was splitting his country, while the co-leader of the Green MEPs, Ska Keller, said the result was "a devastating blow to democracy in Turkey".