An investigation has been launched into the death of Deputy Prime Minister Ahmad Zahid Hamidi's son-in-law Syed Alman Zain Syed Alwi, Health Minister Dr S Subramaniam said today.

The investigation, he added, is to determine the cause of death.

However, the minister said it was too premature to make a conclusion and advised people not to speculate on the incident.

"The investigation started yesterday. It is still too early to make a conclusion (as to what happened)," Subramaniam is quoted as saying by Bernama.

Syed Alman Zain, who was the husband of Ahmad Zahid's eldest daughter Nurulhidayah, passed away in Bangsar yesterday.

The deceased was reported to have gone to a dental clinic with a friend around 6pm for treatment when he became unconscious.

A family member said Syed Alman Zain was rushed to University Malaya Medical Centre, where he was confirmed to have breathed his last.

His remains were laid to rest at the Sungai Ramal Luar Muslim cemetery in Kajang this morning.

Earlier, Prime Minister Najib Abdul Razak and his wife Rosmah Mansor were at Surau An-Nur, Country Heights, to pay their last respects to the deceased prior to the funeral prayers performed by hundreds of Muslims who had gathered there.

The prime minister also expressed his condolences to Ahmad Zahid and his family on their bereavement.

"Semoga roh Allahyarham dicucuri rahmat. Al-Fatihah," said Najib in his Twitter and Facebook.

The deputy prime minister has just returned to Malaysia after a working visit to Japan.

He and his wife Hamidah Khamis were on hand to receive Najib and Rosmah when they arrived at the surau at 8.45am.

Others who attended the funeral were Sarawak governor Abdul Taib Mahmud’s wife Ragad Kurdi Taib, Malacca Chief Minister Idris Haron and Minister in the Prime Minister's Department Jamil Khir Baharom.