Campaigning formally started Saturday for Malaysia's May 9 general elections that will determine if scandal-plagued Prime Minister Najib Razak's coalition can extend nearly 61 years of unbroken rule against an unprecedented challenge led by nonagenarian former strongman Mahathir Mohamad.
Scores of election candidates submitted nomination papers at their home constituencies, paving the way for the start of an 11-day campaigning period.

Malaysian Prime Minister Najib Razak, second from left, and his wife Rosmah Mansor wave to supporters while walking toward the election nomination center in Pekan, Pahang state, Malaysia, Saturday, April 28, 2018. (AP Photo/Sadiq Asyraf)
Najib, escorted by hundreds of supporters waving party flags, filed his nomination in Pekan in central Pahang state. Mahathir, who was one of Asia's longest serving rulers for 22 years until his retirement in 2003, registered to run in the northern resort island of Langkawi.
About 15 million Malaysians will cast ballots to fill 222 seats in federal Parliament and choose representatives for 12 state legislatures.
"It is another test of Najib's survival. He has so far emerged unscathed in all the challenges presented to him in the last few years and this is the biggest one of all," said Rashaad Ali, research analyst with S. Rajaratnam School of International Studies in Singapore.

Former Malaysian strongman Mahathir Mohamad, right, shakes hands with other candidates at the nomination center in Langkawi, Malaysia, Saturday, April 28, 2018. (AP Photo/Vincent Thian)
Mahathir made a high-profile return to politics two years ago amid anger over a massive corruption scandal involving the 1MDB state fund, which is under investigation in the U.S. and other countries for allegations of cross-border embezzlement and money laundering. Najib set up and previously led the 1MDB fund when he took power in 2009 to promote economic development, but it accumulated billions in debt.
The U.S. Justice Department says at least $4.5 billion was stolen from 1MDB by associates of Najib and it is working to seize $1.7 billion allegedly taken from the fund to buy assets in the U.S.

A motorcycle passes by an election poster of former Malaysian strongman Mahathir Mohamad in downtown Langkawi, Malaysia, Friday, April 27, 2018. (AP Photo/Vincent Thian)
Najib, who denies any wrongdoing, has taken an authoritarian bent since the scandal emerged by sacking critics in his government and muzzling the media. His National Front coalition currently holds 132 parliamentary seats after support eroded in the last two elections. It lost its supermajority in Parliament in 2008 and in 2013, it lost the popular vote for the first time to the opposition.
Mahathir now leads the four-party Hope Alliance, which currently holds about a third of parliamentary seats and controls two of Malaysia's 13 states.

Former Malaysian strongman Mahathir Mohamad meets with local community in Langkawi, Malaysia, Friday, April 27, 2018. Malaysian general elections that could determine scandal-plagued Prime Minister Najib Razak's political survival were set for May 9, with analysts saying the workday polls may reduce voter turnout. (AP Photo/Vincent Thian)
Analysts expect Najib, 64, to win a third term due to increased gerrymandering following recent electoral boundary changes, a buoyant economy and strong support from rural Malays, the bedrock of support for his coalition in a multi-racial nation that also includes ethnic Chinese and Indian minorities.
The opposition has not managed to gain much ground in eastern Sabah and Sarawak states on Borneo island, which account for a quarter of parliamentary seats.
Analysts say Najib has to win decisively to ward off challenges to his leadership ahead of year-end elections in his ruling Malay party.

Former Malaysian strongman Mahathir Mohamad speaks as he meets with local community in Langkawi, Malaysia, Friday, April 27, 2018. Malaysian general elections that could determine scandal-plagued Prime Minister Najib Razak's political survival were set for May 9, with analysts saying the workday polls may reduce voter turnout. (AP Photo/Vincent Thian)
Najib has extended cash handouts to civil servants and Malays, his key voting blocs, as he urged Malaysians to stick to the National Front "for a greater Malaysia." The economy grew 5.9 percent last year, its strongest in three years, but many Malaysians are upset with a rising cost of living partly due to an unpopular 6 percent goods and services tax introduced in 2015 to bolster government revenue.
Mahathir's opposition pact has promised to axe the goods and services tax and reopen investigations into the 1MDB scandal if it wins. It also pledged to clip the powers of the prime minister, revive a fuel subsidy and abolish tolls.

A small hut is decorated with flags of Malaysia's ruling National Front coalition, or Barisan Nasional in Pekan, Malaysia, Friday, April 27, 2018. Malaysian general elections that could determine scandal-plagued Prime Minister Najib Razak's political survival were set for May 9, with analysts saying the workday polls may reduce voter turnout. (AP Photo/Sadiq Asyraf)

A motorcyclist rides past the flag of Malaysia's ruling National Front coalition, or Barisan Nasional in Pekan, Malaysia, Friday, April 27, 2018. Malaysian general elections that could determine scandal-plagued Prime Minister Najib Razak's political survival were set for May 9, with analysts saying the workday polls may reduce voter turnout. (AP Photo/Sadiq Asyraf)

Flags of Malaysia's ruling National Front coalition, or Barisan Nasional, are displayed in Kuala Lumpur, Malaysia, Friday, April 27, 2018. Malaysian general elections that could determine scandal-plagued Prime Minister Najib Razak's political survival were set for May 9, with analysts saying the workday polls may reduce voter turnout. (AP Photo/Jeffrey Ong)

Flags of Malaysia's ruling National Front coalition, or Barisan Nasional, are displayed in Kuala Lumpur, Malaysia, Friday, April 27, 2018. Malaysian general elections that could determine scandal-plagued Prime Minister Najib Razak's political survival were set for May 9, with analysts saying the workday polls may reduce voter turnout. (AP Photo/Jeffrey Ong)