ANKARA (Reuters) - Turkey’s prime minister called on voters on Saturday to back a change to the constitution in an April referendum that would greatly strengthen President Tayyip Erdogan’s powers, portraying the reform as a vote for stability.

Thousands of ruling AK Party members waved Turkish flags and rallying songs resounded around a packed sports arena in the capital as Prime Minister Binali Yildirim handed out red carnations and kicked off the campaign for a Yes vote in April.

“There is a rising voice from the town squares: for a strong Turkey, for lasting stability our decision is ...” Yildirim called out earlier to thousands who couldn’t get into the full stadium, eliciting the shouted response “Yes”.

The bid to replace the EU candidate country’s parliamentary democracy with a powerful executive presidency is seen by Erdogan supporters as a guarantee of stability, preventing a return to the fragile coalitions of previous decades.

But opponents fear a surge in authoritarianism.

Tens of thousands of people have already been detained and more than 100,000 public sector workers suspended or dismissed since an attempted coup last July.

The NATO member of 80 million people will vote on the reform in a plebiscite on April 16, with a simple majority needed to approve legislation passed by parliament in January and rubber-stamped by Erdogan last month. [L5N1FV2IZ]

Erdogan says an overhauled political system is needed to tackle unprecedented security threats, from a series of Islamic State and Kurdish militant bombings to the putsch during which rogue soldiers killed at least 240 people.

“The new system will bring the end of terror, it will destroy terror,” Yildirim said, saying Kurdish militants, Islamic State and supporters of the U.S.-based cleric accused of orchestrating the failed coup all sought a “No” vote.

PM REJECTS POLARIZATION

Erdogan has said voting against the change means siding with supporters of terrorism, but Yildirim sought to assuage concerns about a divisive campaign, saying the AKP aimed to unite rather than polarize and would reach out to opposition supporters. The nationalist MHP opposition supports the reform.

Erdogan, the most popular but also most divisive politician in modern Turkish history, has long cast himself as the champion of ordinary, pious Turks exploited by a secular elite. But some pollsters and people close to the AK Party now think his polarizing rhetoric risks scaring off moderate voters in April.

The AKP, which Erdogan founded, has been in power since 2002, and he became prime minister in 2003. He won the largely ceremonial post of president in 2014 and pushed its powers to the limit. The reforms could keep him in office until 2029.

The legislation enables the president to issue decrees, declare emergency rule, appoint ministers and top state officials and dissolve parliament. The two largest opposition parties say the proposals would remove the balances to the already considerable influence Erdogan wields over government.

Uncertainty generated by the political overhaul has worried investors already unnerved by a slowing economy, a volatile lira and a deteriorating security environment. But Yildirim said the reform would provide an economic boost.

“With the new system, the economy will advance on a stronger, more solid and healthier basis. With stability, investment, production and employment will increase,” he said.