Prime Minister Dr Mahathir Mohamad has expressed confidence that the bill to amend the Federal Constitution to lower the voting age to 18 will receive two-thirds majority support from MPs.

He said this after a briefing specifically for opposition MPs - possibly the first in history - on the government's plans to incorporate opposition requests into the bill.

Mahathir said opposition MPs had pledged their commitment to support the bill on condition that the new law would allow those over 18 to be automatically included in the voter register and that the age for election candidates also be lowered to 18.