Georgia's parliament has overwhelmingly approved a controversial amendment to the constitution that will shift primary political powers from the president to the prime minister.

In a 112-5 vote, with one deputy abstaining, lawmakers approved a series of changes to the constitution that its supporters say will introduce more checks and balances in Georgia's political system by curbing presidential powers and beefing up the role of the prime minister and the parliament.

"We now have a constitution that moves us from a presidential-parliamentary model to a parliamentary-presidential model, in which the president is more of an arbiter than someone who carries out domestic policy, as has been the case until now," said Levan Vepkhvadze, the parliament's deputy speaker.

Saakashvili introduced the constitutional reform process last year, seeking to portray it as an attempt to bridge the gap between the ruling authorities and an increasingly hostile opposition.

Critics say the new constitution paves the way for him to retain power as prime minister after he steps down as president.