Saudi Arabia's King Abdullah bin Abdulaziz died on Friday and was replaced by Crown Prince Salman, the OPEC-kingpin's royal court said in a statement.

The late monarch's half brother Moqren was named crown prince, according to the statement.

King Abdullah, 90 had been in hospital for a few weeks suffering from a lung infection.

In 2005, Abdullah came to the throne but had suffered frequent bouts of ill health in recent years.

King Salman, 79, had recently taken on the ailing monarch's responsibilities.

The late king's half brother Moqren has been named the new crown prince, the official statement said.

King Salman called on the royal family's Allegiance Council to recognise Moqren as his crown prince and heir.

"His Highness Salman bin Abdulaziz Al Saud and all members of the family and the nation mourn the Custodian of the Two Holy Mosques King Abdullah bin Abdulaziz, who passed away at exactly 1am this morning," the statement said.

In recent years, his advanced age and poor health had raised concerns about the future leadership of one of the world's key oil producers.

Abdullah's half-brother Salman, 79, was named crown prince in June 2012 following the death of Prince Nayef bin Abdulaziz.

Salman had been representing the king at most recent public events because of the monarch's poor health.

In March 2014, King Abdullah named his half-brother Prince Moqren as a second crown prince, in an unprecedented move aimed at smoothing succession hurdles.

Moqren, who was born in 1945, is the youngest of Abdulaziz's sons.

Since the death in 1952 of King Abdulaziz al-Saud, the founder of Saudi Arabia, the throne has systematically passed from one of his sons to another.

But many of them are old or have died. The former crown princes Sultan and Nayef died in 2011 and 2012 respectively.