Malaysian Prime Minister Najib Razak, facing a robust challenge from the opposition ahead of Wednesday's general election, offered voters three policy promises if they return him to power, including the exemption of young people from income tax.

"These promises prove that we are not a bankrupt country or a failed state. A bankrupt country or a failed state would not be able to announce such measures," Najib said at his final campaign rally late on Tuesday.

"Malaysia is a successful country... I want all Malaysians to wake up to a happy Malaysia," he said in a speech that was carried live on national television.

Najib said that if his Barisan Nasional (BN) coalition wins the election, people aged 26 and under would no longer pay income tax and any that had paid in the past would be reimbursed.

He also promised to add two public holidays at the beginning of Ramadan, which starts next week, and said toll roads would be free for a period of five days starting two days before the Eid festival, which marks the end of the holy month.

Merdeka Center, an independent polling firm, said earlier on Tuesday that Najib's coalition had lost ground in the lead-up to the election, but could still win enough parliamentary seats to cling on to power.

Scandal-hit Najib, whose BN alliance has ruled Malaysia for more than six decades, is pitted in a fierce contest against his mentor-turned-foe Mahathir Mohamad, who was prime minister of the Southeast Asian nation for 22 years.

Mahathir gave his last campaign speech at the same time as Najib. His rally was not broadcast on television but was livestreamed on the Internet.