Malaysia's king has abdicated, royal officials said on Sunday, in a historic first for the country that ended weeks of speculation about his future after he took medical leave.

Sultan Muhammad V's decision marks the first time a king has abdicated in the Muslim-majority country since it gained independence from Britain in 1957.

It came after the king took leave at the start of November for two months, during which time unconfirmed reports circulated that he had married a Russian former beauty queen.

A statement from the national palace confirmed the resignation of the relatively youthful monarch, known for his fondness for four-wheel driving and other extreme sports.

"His majesty tells the people of Malaysia to continue to be united to maintain unity, tolerance, and work together," said the statement, signed by the Comptroller of the Royal Household, Wan Ahmad Dahlan Abdul Aziz.

It gave no reason for the 49-year-old's move.

But there had been a question mark over the reign of the king, who ascended to the throne in December 2016, since he took a leave of absence for medical treatment in November.

Reports then circulated online that he had married a former Miss Moscow in Russia.

Royal officials in Malaysia have so far not commented on the rumoured marriage, or given any details about his health condition.

While their role is ceremonial, Malaysia's Islamic royalty command great respect, especially from Muslim Malays, and criticising them is strictly forbidden.

Speculation intensified about the king's future this week when the country's Islamic royals reportedly held a special meeting.

Malaysia is a constitutional monarchy, with a unique arrangement where the throne changes hands every five years between rulers of the nine Malaysian states headed by centuries-old Islamic royalty.

The rotating monarchy system has been in place since independence from Britain in 1957, and Sultan Muhammad V is the first monarch to have renounced the throne.

Sultan Muhammad V studied at St Cross College at Oxford and the Oxford Centre for Islamic Studies, according to official media.

He is known for a relaxed public persona, taking part in walkathons to promote health, and has been photographed wearing a baseball cap backwards.

Portraits of the king and queen adorn government buildings throughout the country. The king is also the symbolic head of Islam in the nation, as well as the nominal chief of the military.

Malaysia's sultans trace a lineage back to Malay sultanates of the 15th century. The king is referred to as Yang di-Pertuan Agong, or "He Who Is Made Lord".