Malaysia's Prime Minister Najib Razak said he was shocked by the death of veteran opposition politician Karpal Singh.

"I am shocked to hear of Karpal Singh's tragic passing," Mr Najib said in a statement issued by his office.

"In a career that spanned five decades, Karpal's abilities made him a formidable opponent.

"In politics, he was an implacable leader; in law, a committed advocate," Mr Najib said.

"At this difficult time, our thoughts are with the families of those who have died in the accident. I extend my deepest condolences to them. We pray that the other passengers make a full recovery," the statement added.

Earlier, Mr Najib expressed his condolences to Mr Karpal's family via Twitter from Turkey.

"I have just landed at Ankara when I heard the news that YB Karpal Singh died in a road accident. My condolences to the family," he tweeted.

Mr Karpal, 73, Member of Parliament for Bukit Gelugor and veteran Democratic Action Party (DAP) leader, died in an accident on the North-South Highway near Gua Tempurung, Perak, early on Thursday morning.

The prominent lawyer and his assistant C. Michael died at the scene. Mr Karpal's son Ramkarpal and the car's driver C. Selvam were injured in the incident, which took place at 1am.