Turkish President Tayyip Erdogan has approved a constitutional reform bill paving the way for an executive presidential system, his office said on Friday, and a deputy prime minister said a referendum on the issue was expected on April 16.

Erdogan says the reform will provide stability at a time of turmoil and prevent a return to the fragile coalitions of the past. His opponents fear it will herald increasingly authoritarian rule.

A brief statement on the presidency web site said the bill had been sent to the prime minister's office to be published and submitted to a referendum.

"With the president's approval, eyes are now on the YSK (High Election Board). The YSK will probably announce that April 16 is the appropriate date for a referendum," Deputy Prime Minister Numan Kurtulmus told reporters.

Parliament approved the bill last month after securing more than the minimum 330 votes in the 550-seat assembly. If the legislation is approved in the nationwide vote, it could pave the way for Erdogan to remain in office until 2029.

The reform would enable the president to issue decrees, declare emergency rule, appoint ministers and top state officials and dissolve parliament - powers that the two main opposition parties say strip away balances to Erdogan's power.