ISTANBUL (AFP) - Turkey's political and business elite on Sunday made a rare show of unity to turn out in force at the funeral of the head of Turkey's biggest family-run industrial conglomerate, Mustafa Koc, who died last week aged only 55.

President Recep Tayyip Erdogan, Prime Minister Ahmet Davutoglu and main opposition Republican People's Party (CHP) leader Kemal Kilicdaroglu were among the mourners at the funeral at an Istanbul mosque for the Koc Holding CEO, who died on Thursday after a massive heart attack.

Koc was the leader of the third generation of the dynasty founded by his grandfather Vehbi Koc in the 1920s and which now has interests in energy, finance and autos grouped together under Koc Holding.

Mustafa Koc took over as chief executive of Koc Holding in 2003 after the retirement of his father Rahmi Koc, now 85, who survives his son.

Mr Rahmi Koc greeted the mourners along with his younger son Ali Koc in front of the coffin draped in a banner with an inscription in Ottoman Turkish script. The coffin also bore a ribbon from the family's favourite football team, Fenerbahce of Istanbul.

Turkey's family-run conglomerates are the mainstays of the country's economy with interests in every sector. Koc Holding alone accounts for around 9 per cent of Turkish exports and 8 per cent of its GDP.

Prominent Turkish businessmen also made rare public appearances at the funeral.

"Mustafa Koc is an incredible loss. Look at the size of the crowds here," banking tycoon and FIBA Holding founder Husnu Ozyegin told NTV television.

Mustafa Koc was respected in business circles for presiding over sustained growth at Koc Holding. But he also won admiration from Turkish liberals with support of anti-government protesters in 2013.

Koc allowed protesters in Taksim Square in Istanbul to take refuge in the nearby Divan Hotel, which is owned by the group, infuriating Mr Erdogan who criticised Koc for harbouring "criminals".

The group then found itself the target of probes over alleged tax violations.

But the Turkish President on Friday paid warm tribute to Koc, revealing that he had held talks with the businessman in Ankara just a day before he died.

"We even joked. We talked about weight loss issues. And I even quipped 'did you cut down on alcohol? It's time to stop completely'," said the pious president.

Mustafa Koc was buried in the family plot at the Zincirlikuyu cemetery in Istanbul, next to his grandfather Vehbi Koc.