Malaysian former Prime Minister Mahathir Mohamad has been admitted to hospital for fatigue, his office said on Sunday, after media reported he had left a picnic celebration for his 100th birthday early.

Mahathir, leader of the Southeast Asian nation for more than two decades, has a history of heart problems and has undergone bypass surgeries. He has been hospitalised repeatedly in recent years, most recently in October for a respiratory infection.

He is under observation at the National Heart Institute in Kuala Lumpur for fatigue-related issues, his office said. "He is resting, but we expect him to be back home by this evening," it said in a statement.

A physician who was a member of parliament until 2022, Mahathir drove himself on Sunday to the celebration, which also marked the 99th birthday of his wife, Hasmah Mohd Ali, a day earlier, local media reported. The reports said he cycled for an hour before appearing tired. His birthday was on Thursday.

Mahathir was prime minister for 22 years until 2003. He returned as premier in 2018 after leading the opposition coalition to a historic win, but his government collapsed in less than two years due to infighting.