KUALA LUMPUR, May 8 (Xinhua) -- Leaders of Malaysia's political parties are making their last efforts on the last day of campaign ahead of Wednesday's polling for the country's highly-contested election.

The official campaign period will end by midnight on Tuesday before Malaysians go to the ballot box on Wednesday.

Both Najib Razak, the incumbent Prime Minister who leads the ruling coalition Barisan Nasional, and Mahathir Mohamad, the former Prime Minister who heads the opposition against his former camp, are expected to spend the last day before the election at their own constituencies, respectively.

The two are both scheduled to give speeches in the evening in the last bid to win voters.

The 92-year-old Mahathir, despite his advanced age, has been touring in the country during the campaign, calling for change after 60 years of uninterrupted governing by the ruling coalition in the country since independence.

In a televised interview and an article published in his blog on Monday, Najib stressed the track record of his government since he came to office in 2009.

"The average growth of 5.4 percent since 2010, which the world's advanced economies could only wish for," he said in the article.

"The Gross National Income up by over 50 percent, which represents a huge increase in the national wealth, and explains why the International Monetary Fund commends us for being well on the way to high income status."

He also defended the introduction of the Goods and Services Tax (GST), which the opposition blamed for the rise of living cost and has since vowed to abolish.

"Introducing the GST was one of the hardest decisions I have made. I knew that it would lead to some increases in the prices of some goods and services, and that it would be painful for some Malaysians," he said.

"But I also knew that without GST, our economy would continue to be overly reliant on the price of oil."

Abdul Wahid Omar, group chairman of the investment management company PNB and a former cabinet minister, argued that the costs have gone up with the growing economy, but the inflation was still lower than the household income growth.

Abolishing GST and reverting back to a Sales and Service Tax is a regressive move, Wahid said, which will affect the government's ability to implement the various infrastructure projects and other people friendly programs.

"It may also potentially result in Malaysia's credit rating to be downgraded should the Government's budget deficit increase above the 3 percent level achieved in 2017," he told Xinhua in a written interview.

Tay Tian Yan, deputy executive editor-in-chief of the local Sinchew Daily, said many were discontented by the GST although it was considered a more sensible and fair tax.

The ruling collation was widely favored ahead of election, but it became a close race in the run up to the polling day.

By accepting Mahathir, the opposition coalition hope the former Prime Minister could break into ruling coalition's stronghold in the rural area and among the ethnic Malay voters, who account for the majority of the country's population, said Tay.

In his article, Najib said Mahathir and the opposition were trying to use each other.

Mahathir, Malaysia's longest-serving prime minister from 1981 until 2003, fell out with Najib after he accused the incumbent prime minister of corruption in relation to the state investment fund 1MDB. Najib has denied any wrongdoing.

Mahathir later joined the opposition and became its candidate for Prime Minister.

The election on Wednesday will see 15 million voters vote for 222 seats of the lower house of the parliament and 505 seats of the state legislations.