Defeated at the polls two weeks ago, Najib was summoned to explain suspicious transfers of $US10.6 million into his bank account, just a fraction of billions of dollars that went missing from 1Malaysia Development Berhad (1MDB), a state fund that he had founded during almost a decade in power.

The new government led by 92-year-old Mahathir Mohamad has vowed to find out where the 1MDB money went and punish those responsible.

Najib has denied wrongdoing, though the new head of the Malaysian Anti-Corruption Commission (MACC) this week described how an investigation into 1MDB had been suppressed three years ago to stop charges being brought against him.

Najib, 64, appeared relaxed as he left the MACC headquarters some seven hours after arriving. Smiling, he put a finger to his lips to shush journalists so that he could speak.

"I have answered all questions as best as I could, and MACC has carried out their duties well and professionally," Najib said.

He said the MACC had told him the "statement-session" was over.

Malaysians are now wondering if charges will be filed. The new government has barred Najib and his wife, Rosmah Mansor, from leaving the country.

Najib's statement relates to the transfers of 42 million ringgit ($US10.6 million) into his bank account that investigators tracked back to SRC International, a former unit of 1MDB.

Mahathir quit as prime minister in 2003 after leading Malaysia for 22 years, but came out of retirement to join the opposition after becoming convinced that Najib, his former protege, was corrupt.

Investigators have searched Najib's home and several properties, seizing cash, jewellery and luxury items estimated to be worth tens of millions of dollars.

Mahathir has accused Najib's government of understating the national debt and blamed it for abuses that have caused debt to balloon.

Finance Minister Lim Guan Eng said Najib's government had committed to making lease payments of 201.4 billion ringgit ($US50.62 billion) for several projects designed to circumvent the federal government guarantee and debt limits.

The extra obligations brought Malaysia's total debt and liabilities to over 1.087 trillion ringgit as of December 31, 2017, or 80.3 per cent of gross domestic product, Lim told reporters.

Earlier this week, Lim said the Najib government had deceived the public and parliament over the country's finances and 1MDB.

In a late night Facebook post on Wednesday, Najib said Mahathir and his finance minister's "alarming and confusing" remarks about the country's debts and 1MDB liabilities "tell half the story".

"While you may want to slander and put all the blame on me to give a perception of a dire financial position to justify why you cannot deliver on your manifesto promises ... you must remember that the country and our people come first," he wrote.

Australian Associated Press