The ruler of Dubai, Sheikh Maktoum bin Rashid al-Maktoum, has died aged 62 while visiting Australia, the United Arab Emirates (UAE) has announced.
The official statement did not indicate the cause of death
Sheikh Maktoum was also vice-president and prime minister of the UAE, a federation of seven Gulf states.
Internationally, he was known as co-owner of Dubai's Godolphin stables, which competes in major horse races.
His brother, Crown Prince Sheikh Mohammed bin Rashid al-Maktoum, has succeeded him as ruler of Dubai.
Sheikh Mohammed has been the UAE defence minister since 1971 and heir apparent to the throne of Dubai since 1995.
He has been largely responsible for the phenomenal growth and development of the city in recent years, but with Sheikh Maktoum's blessing.
The BBC's Julia Wheeler in Dubai says Sheikh Mohammed is one of the most formidable and impressive sheikhs within the UAE, something which has sparked envy as well as admiration by some in other emirates.
The UAE's supreme council must approve a successor to Sheikh Maktoum as vice-president and prime minister of the federation. This may happen as early as Thursday.
There has been a long term understanding that both posts are held by Dubai, although officials say the constitution does not specify this, our correspondent says.
Sheikh Maktoum was staying at a luxury hotel on Queensland's Gold Coast when he died.
"The United Arab Emirates today lost a historic leader who devoted his life to establishing the United Arab Emirates and enhancing its structure and the welfare of its people," a statement from the UAE's presidency said.
The Ministry of Presidential Affairs from the neighbouring emirate of Abu Dhabi said Sheikh Maktoum had "placed his country's interest over any other considerations".
"He was a model of good behaviour," the statement added.
Forty days of national mourning have been declared.
Sheikh Maktoum maintained a low profile, preferring to allow his younger brothers to run the daily affairs of Dubai.
The statement did not indicate the cause of death.
Sheikh Mohammed has been Dubai's heir apparent since 1995
Queensland Police spokeswoman Chelsea Roffey said the Dubai ruler died at the Palazzo Versace hotel, where rooms cost up to $2,600 per night.
He had arrived in Australia on 28 December.
Sheikh Maktoum's body is expected to be flown back to Dubai from Brisbane on his private Boeing 747-400 later on Wednesday.
Sheikh Maktoum was well-liked in Dubai and his death will come as a shock to many.
But his death is unlikely to change the direction of policy either in Dubai or in the UAE, our correspondent adds.