Its running of the election has been criticized by both opposition and ruling party figures. But some analysts said voter turnout could be lower due to mid-week voting.
Malaysians will elect 222 Members of Parliament and representatives for 505 state seats nationwide, from a total of 2,333 candidates, who filed their nomination papers on April 28.
Election Day is expected to be busy: at more than 8,200 polling places around the country.
To see why, start with my analysis of the last election, in 2013. The Election Commission and government dismissed the charges. "Many were out early to cast their ballot".
Polling stations closed at 0900 GMT on Wednesday. Phantom voters, electoral roll tampering, power blackouts during vote counting, widespread cheating, gerrymandering, etc. have been worrying the opposition parties and civil society groups. He urged voters to ignore "fake" messages aimed at creating panic. "BN is far behind and there's no way they can catch up", Mahathir was quoted to have said at around 11:30pm local time. He said the incidents are isolated and the commission will investigate. "That's all I see", said Mohamad Muda, a 69-year-old fisherman from Pekan in Pahang state.
Angered by the corruption scandal that engulfed the state investment fund set up and overseen by Najib, Mahathir defected from the ruling coalition's dominant United Malays National Organization party and joined forces with opposition parties who had regarded him as their chief nemesis.
Dr Mahathir, who won his parliamentary seat in Langkawi, Kedah with 44.4 per cent of the vote, added that people must know what's their duty and must do according to what's right according to the constitution. "People are for people".
"The prime minister's speech is the flawless reverse-image of the political reality of Malaysia", said Dr. Sophie Lemiere, a political anthropologist at Harvard University.
Heading into Wednesday's polls, he was facing a stiff challenge from his 92-year-old former political mentor, Mahathir.
"I feel very good, I am confident unless Najib cheats".
He urged Malaysians to vote based on facts.
Research firm Capital Economics said in an April note that Najib's chances will be improved by "years of gerrymandering" that will make it easier for the government to collect a majority.
"It is the Pakatan government", the former prime minister told reporters, referring to his comeback bid to replace the government of Barisan Nasional chairman Datuk Seri Najib Razak.
Morning newspaper headlines focused on Najib's election eve promises of tax exemptions for young people, extra public holidays and a five-day break from road tolls if his coalition wins.
The defeat is a humiliating fall from grace for Najib, the scion of one of Malaysia's most prominent political families, and his coalition party, Barisan Nasional, which had led the country since its independence 61 years ago.
Liow Tiong Lai, president of Malaysian Chinese Association, lost his seat in Bentong, Pahang state, and S. Subramaniam, president of the Malaysian Indian Congress, did not win his constituency of Segamat, Johor state.