King of Tonga, George Tupou V, died on Sunday in Hong Kong at the age of 63. The Tongan government confirmed the death with the media but did not reveal a cause.

Tupou, who played a key role in bringing democratic reformation to the South Pacific nation, died hours after being rushed to the hospital. The Matangi Tonga Online reported that the king's younger brother, Crown Prince Tupouto'a Lavaka, was by his side.

Tupouto'a Lavaka will succeed his brother as he is heir to the throne.

Tonga has just woken up to the sad news of the passing of King George Tupou V, Paula Ma'u, an official in the Ministry of Information and Communication, told CNN. We are all in mourning.

The Agence France-Presse reported that the king underwent surgery last year in Los Angeles to remove a kidney after a cancerous tumour was found.

Tupou was a bachelor. He was sworn in as king of Tonga in September 2006 after his father, King Taufa'ahau Tupou IV, died, according to the Global Post.

Before sitting on the throne he was known for his globe-trotting lifestyle and extravagant uniforms.

CNN reported that Pesi Fonua, editor of Matangi Tonga online, said that the Oxford-educated king was respected for the efforts he made to bring democratic reforms and modernize Tongo.

This king brought in things like mobile phones and other advances that we couldn't dream would come to Tonga, and his push for democracy made a big impact on the people here, Fonua said.

The BBC reported that mourning has begun and that a state funeral is being organized.