Malaysians went to the polls on Wednesday in one of the country's closest ever elections which pits scandal-hit Prime Minister Najib Razak against his one-time mentor, a 92-year-old former authoritarian leader.
Najib is seeking to retain power at the head of a regime that has ruled Malaysia since independence in 1957, but veteran ex-leader Mahathir Mohamad's shock comeback has upended the election race.
Angered by a scandal at state fund 1MDB that battered Malaysia's international standing, Mahathir has teamed up with an alliance of parties that fiercely opposed him when he was in power, and which includes jailed opposition icon Anwar Ibrahim -- his former nemesis.
Najib's ruling Barisan Nasional coalition is expected to triumph due to what critics claim is manipulation of the electoral system.
It also benefits from the benchmark for victory, which requires only that it wins a simple majority of MPs in parliament, rather than the popular vote.
It is however expected to be a tight race and the opposition alliance has gained ground in recent weeks as Mahathir, who ruled with an iron fist for 22 years, has chipped away at the government's key support base, the Muslim Malay majority.
Polls opened at 8:00 am (0000 GMT), with people starting to stream to voting centres across the country, and were due to close at 5:00 pm (0900 GMT). Results are expected to be known late on Wednesday.