KUALA LUMPUR (Reuters) - With just a week to go to a general election, Malaysia’s main opposition bloc is making gains and will likely win the popular vote, but Prime Minister Najib Razak is expected to retain power, according to a survey by pollster Merdeka Center.

Malaysia's Prime Minister Najib Razak speaks during an election campaign rally in Kuala Lumpur, Malaysia May 1, 2018. REUTERS/Lai Seng Sin

Malaysians vote on May 9, with Najib going up against his former mentor turned critic Mahathir Mohamad, a former long-serving prime minister now leading the opposition.

Najib is facing his toughest election yet as he grapples with public anger over rising costs and a financial scandal at a state fund.

Mahathir’s Pakatan Harapan coalition is likely to win 43.7 percent of the popular vote, as of May 1, up from a forecast of 42 percent, as of April 9, Merdeka Center director Ibrahim Suffian said on Wednesday.

Najib’s Barisan Nasional (BN) coalition is expected to win 40.3 percent of the popular vote, as of May 1, down slightly from an April 9 forecast of 40.8 percent, Ibrahim said.

The Merdeka Center is one of Malaysia’s few independent pollsters.

The poll was conducted in west Malaysia, which accounts for nearly 75 percent of parliamentary seats. It did not include the Malaysian part of Borneo island.

Support for Parti Islam se-Malaysia (PAS), another opposition party that is not part of Mahathir’s coalition, dropped from 17.2 percent in April to 16 percent as of May 1.

“If elections were held yesterday, BN would still prevail,” Ibrahim said in a presentation streamed live on Facebook, referring to the ruling coalition which has held power since independence from Britain in 1957.

Najib’s coalition failed to win the popular vote in the last elections in 2013, getting 47.3 percent of the votes in what was seen as a setback for the ruling alliance even though it retained power.

Under Malaysia’s first-past-the-post, or simple majority, system the party that gets the most seats in parliament wins even if it does not win the popular vote.

A worse performance for the BN coalition than in 2013, even if it retains power, would likely raise questions within the ruling bloc about Najib’s leadership.

Support for Mahathir’s opposition alliance among majority ethnic Malays has increased, with the gains coming at the expense of the PAS, not the BN, Ibrahim said.

“In the last two weeks, Malay numbers have started to shift,” Ibrahim said.

He also said he could not predict the number of seats each party would win as the “voting patterns have gotten complex”.

The opposition and other critics have said recently redrawn electoral boundaries favor the BN, which has been accused of gerrymandering.

BN and the Election Commission have rejected that, saying the changes were made independently and without any political interference.