Malaysia's King Muhammad V resigned on Sunday, the first time a monarch has stepped down from the throne in the country before completing their five-year tenure.

Muhammad V's resignation took effect immediately, the National Palace said in a statement. It did not give a reason for the 49-year-old royal's abrupt move.

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

Malaysia has nine royal households that typically take turns to be king. The selection of the next monarch can be decided by a vote in the Council of Rulers, made up of all nine royal households.

The palace statement said the king was grateful for the opportunity given to him by the Council of Rulers and thanked the prime minister and government.

"His Highness has worked towards fulfilling his responsibilities entrusted to him as the head of state, serving as a pillar of stability, source of justice, the core of unity ... for the people," the palace said.

The resignation comes barely a week after the king resumed his duties after spending two months away on medical leave.

Images purporting to show the king getting married in Russia appeared on social media in December.

He is said to have married a 25-year-old former Russian beauty queen in November. The reports in Russian and British media and on social media featured pictures of the wedding, which reportedly took place in Moscow.

The palace did not respond to requests for comment on the photos or reports of a marriage.