Oil-rich Brunei’s absolute ruler marked 50 years in power on Thursday, with elaborate celebrations that included a glittering procession through the capital on a gilded chariot.

Sultan Hassanal Bolkiah, 71, is now the world’s second-longest reigning monarch, after ascending the throne in the tiny northeast Borneo nation in 1967.

Dressed in gold brocade, the sultan entered the capital, Bandar Seri Begawan, with his wife, Queen Saleha, and their children on a carriage pulled by 50 members of the royal household clad in traditional black and gold woven cloth.

A military band led the five-km (three-mile) procession, which was greeted by more than 80,000 well-wishers, some of whom had arrived as early as 5 am to secure a good spot.

The procession was part of a month-long celebration of the golden jubilee, which includes the opening of Brunei's first cable-stayed bridge, the unveiling of a major new urban park and a state banquet at the gold-domed palace on Friday, attended by regional leaders as well as British and Middle Eastern royalty.

Brunei's Sultan Hassanal Bolkiah waves to people as he passes in a procession to mark his golden jubilee of his accession to the throne in Bandar Seri Begawan on Oct 5, 2017. - REUTERS
"The responsibility of the king is to his people and the people have a responsibility to the king," the sultan told an audience at the palace. "Together, the king and the people hold the trust of the nation."

Brunei, a former British protectorate of about 400,000 people, relies heavily on oil and gas exports for its wealth.

The country does not hold elections but any discontent is assuaged with generous government polices, including zero taxes, subsidised housing and free healthcare and education.

Despite tight social controls, the sultan is hugely popular. His rule has seen Brunei gain full independence from Britain and living standards soar to among the highest in Asia.

"When we go to Friday prayers at the mosque, he is there. We can go up to him and shake his hand or pass him letters if we have complaints,” said Aizzat Bakar, 32, a businessman working in the capital.

But the sultan also presided over the adoption of tough Islamic law in 2014, which raised concerns among tens of thousands of non-Muslims, including Western expatriate workers.

The sale of alcohol is banned in Brunei and evangelism by other religions is strictly forbidden.

Details of the lavish lifestyle of the sultan’s brother, Prince Jefri, including owning hundreds of luxury cars and a yacht, became public during a family feud, grabbing global headlines and shocking many in the country.

The sultan, once the world's richest man, has a firm grip on power, but Brunei has also become a microcosm of the trouble faced by oil-dependent states.

As global energy prices tumbled over the past three years, government revenue nosedived by 70 per cent. Brunei is the only Association of Southeast Asian Nations (ASEAN) country to have seen a recession for three straight years.

The price collapse prompted Brunei to embrace Chinese investment, with Beijing pumping billions into key infrastructure projects.

In return, the sultanate has remained largely silent on Beijing’s vast territorial stake in the South China Sea, which overlaps Brunei’s own claims in the disputed waters.