More than 70 per cent of voters have cast their ballots after polls closed at 5pm on Wednesday (May 9) for Malaysia's hotly contested election.

There are some 15 million registered voters who will decide the fate of 222 parliamentary seats and 505 state seats up for grabs.

The ruling Barisan Nasional coalition is up against Pakatan Harapan opposition coalition and Parti Islam SeMalaysia.

What are the possible outcomes, and what do they mean for Malaysia? Here's what you need to know.

1. What happens on May 9?

Malaysians head to their voting centres where they can cast their votes from 8am to 5pm.

They will be choosing their Member of Parliament and state assemblyman. Voters in Sarawak, which held state assembly elections in 2016, will only be choosing their MP.

2. Who's fighting whom?

Ruling coalition Barisan Nasional faces off against the opposition coalition Pakatan Harapan (PH). PH will use the Parti Keadilan Rakyat (PKR) logo - two white crescents on a blue background, resembling an eye.

PH's former ally, the Islamist party Parti Islam SeMalaysia (PAS), will be taking part in three-cornered fights which analysts say should benefit BN.

Helming BN is Prime Minister Najib Razak, 64, who will be facing off against his former-mentor-turned-foe Mahathir Mohamad, 92, who now heads the opposition.

The third leader in the fight is PAS president Abdul Hadi Awang, 70.

3. What are they gunning for?

A simple majority in the federal parliament and control of the state assemblies.

To control Parliament, BN or PH needs to win 112 of the 222 seats. BN had 131, PH had 72, PAS had 13, and PH ally Parti Warisan Sabah had two.

The independent Parti Sosialis Malaysia held one seat, and there were also three independent MPs.

BN controls 10 of the 13 state assemblies. PH runs Penang and Selangor, and PAS runs Kelantan.

4. What could happen?

- BN wins by a wide margin. This is unlikely since it won by a slim margin in 2013, and Dr Mahathir is a formidable opponent who may be able to sway Malay voters who form the backbone of BN's support.

- BN wins by a slim margin. It could maintain power but lose the popular vote, as it did in 2013. This is likely to affect PM Najib's standing in his party and place him on precarious ground afterward.

- Neither BN nor PH win a majority in Parliament. Coalition talks will ensue and anything could happen in the weeks ahead. Elected MPs could be enticed to switch sides, which is allowed under Malaysia's laws.

- PH wins. Any handover will be unpredictable and could be messy, as BN has been the only ruling coalition since independence.

5. When will we know the result?

Results will start trickling in from 9pm. But a fuller picture will only be clear after midnight.