Turkey's parliament on Wednesday embarked on a second round of deliberations on a contentious package of constitutional amendments that would give President Recep Tayyip Erdogan's office executive powers.

Legislators are set to vote separately on 18 proposed amendments before holding a final vote on the whole package by the end of the week.

Debate on the draft amendments that would turn Turkey's parliamentary system into a presidential system has been tense and last week resulted in brawls between ruling and opposition party lawmakers.

The ruling party, founded by Erdogan, argues that a strong presidency is needed to strengthen Turkey as it confronts multiple terrorism threats. Critics say the changes will concentrate too many powers in the hands of Erdogan, who is accused of authoritarian tendencies, and erode checks and balances on his rule.

Erdogan has long pushed for a presidential system saying a strong head of state will thrust Turkey toward its goal of becoming a world power by 2023, when the Turkish Republic marks its centenary. Currently, the presidency is largely ceremonial.

The New York-based advocacy group, Human Rights Watch, urged Turkish lawmakers to reject the constitutional changes.

It said that the proposals would render permanent many of the emergency powers the president had assumed in the wake of a failed July coup to overthrow him.

"The proposed constitutional changes concentrate power in the hands of President Erdogan and further erode already weak checks and balances on the exercise of that power," said Hugh Williamson, Europe and Central Asia director at HRW.

"Parliament should reject these constitutional changes, which would hollow out the rule of law, and profoundly undermine the country's democracy."

Today, Erdogan renewed his support for the amendments that would abolish the office of the prime minister, saying the change will put an end to possible power struggles between the premier and the president who are both popularly elected.

Erdogan became the country's first directly elected president in 2014.

If the reform bill secures at least 330 votes in the 550-seat assembly, it would then be put to a national referendum.