Thailand's king, the world's longest reigning monarch, has called for his countrymen to unite in response to the worst floods in half a century.

King Bhumibol Adulyadej spoke on Monday to mark his 84th birthday, amid deep political divisions plaguing the country.

The king’s speech at the ceremonial Grand Palace lasted for about five minutes after being driven from a nearby hospital where he has been staying for more than two years. Cheering well-wishers lined the route, waving flags and chanting, "Long live the king".

About a fifth of Thailand's 64 million people have been affected by the on-going flood crisis, which began in late July. More than 600 people have died.

Speaking from a terrace to an audience of dignitaries, the king told officials that stability depended upon the happiness of the people, in an address that was also broadcast live nationwide.

Al Jazeera's Wayne Hay, reporting from Bangkok, said there was a visible outpouring of concern for the monarch who is widely seen as a unifying figure in the flood-ravaged nation.

The fact that the ailing king was able to speak live to the people this year, gave many people hope and encouragement for his wellbeing and the country, our correspondent said.

The king who also dispenses royal pardons to around 22,000 convicts will not extend one to Thaksin Shinawatra, the exiled former prime minister of Thailand, a prisons official said.

Political turmoil

Media reports suggested the cabinet had endorsed a draft pardon that could allow Thaksin to return without serving time, but this angered his rivals, and the move was aborted.

Thailand has been in a state of political turmoil since a 2006 military coup ousted Thaksin, setting off a struggle for power between his supporters and opponents.

The battle has sometimes turned violent, culminating with street fighting in the Thai capital last year that saw 90 people lose their lives and several buildings burned down.

A new government led by Thaksin's sister, Yingluck Shinawatra, took office this year after decisively winning elections, relieving some of the political pressure.

In response to the turmoil, the king's occasional speeches in recent years have stressed the need for unity. The king traditionally has played a conciliating role in Thai society, but his declining health and the polarisation of Thai society have hurt his influence.

Bhumibol said it was their duty "to co-operate and fix problems to the best of your ability, especially now that our people are suffering from the floods."

"The most important thing is you should not be split or fighting each other. We need to inspire and give each other confidence so that the work we do will be fruitful for the well-being of the people and the stability and security of the country."

His near-disappearance from the public scene has also raised concerns about what will happen after his passing. His son and heir-apparent, Crown Prince Vajiralongkorn, does not command the same respect and affection.

The king, who took the throne in 1946, was originally taken to hospital in September 2009 with a lung inflammation. Official statements have said he remained at the hospital for physical therapy and nourishment to recover his strength.

Last month, he suffered a health crisis that caused him to temporarily lose consciousness, according to one of his daughters, Princess Chulabhorn. She was told by the doctors the problem could have been caused by his stress over the flooding.