Turkey's parliament approved the first seven articles in a second round of voting overnight on a constitutional bill that will extend President Tayyip Erdogan's powers, keeping the reform on course for a spring referendum.

The two largest opposition parties in parliament say the 18-article bill, which could enable Erdogan to rule until 2029, will fuel authoritarianism in the NATO member and European Union candidate country.

The ruling AK Party, backed by the nationalist MHP, says it will bring the strong executive leadership needed to prevent a return to the fragile coalition governments of the past.

The seven articles approved overnight include increasing the number of MPs to 600 from 550, lowering the minimum age to be a lawmaker to 18 from 25, and holding parliamentary and presidential elections together every five years.

The seventh article opens the way for the president to be a member of a political party. After voting on each of the 18 articles, lawmakers will cast a final vote on the package as a whole.

The voting was expected to be completed on Friday night.

If parliament gives final approval to the constitutional package it will be put to a referendum expected in the spring.

The main opposition CHP and the pro-Kurdish HDP, the second largest opposition party, strongly oppose the changes.

The bill needs the support of at least 330 deputies in the assembly to go to a referendum. The AKP has 316 deputies eligible to vote and the MHP 39. So far articles have generally been approved with at least 340 votes in favour.

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