Dr Mahathir Mohamad has been hospitalised over a chest infection, according to news reports.

He is currently undergoing treatment at the National Heart Institute (IJN) in Kuala Lumpur.

Reports quoted a statement from IJN that the 91-year-old former premier "is expected to be kept under observation for the next few days".

"Tun (Mahathir) is currently admitted in the general ward and based on the medical team's advice, visitation is strictly for close family members only," the statement said.

Mahathir previously underwent a heart bypass operation in 2007, following two heart attacks over the previous two years.

He had undergone the same operation after his heart attack in 1989. After the 2007 operation, he suffered a chest infection. He was hospitalised for treatment of another chest infection in 2010.

This afternoon, former deputy premier Muhyiddin Yassin had submitted an application to register a new party, for which Mahathir would serve as chairperson.

Despite his advanced age, the former premier has been on a campaign to oust Prime Minister Najib Abdul Razak and has been criss-crossing the nation to attend events.

Najib on the other hand has accused his former mentor of conspiring against him.

The prime minister’s supporters claim that Mahathir is attempting to engineer the political ascension of his son Mukhriz, whom he wants to see become prime minister in the future.