A new Saudi anti-corruption body has detained 11 princes, four sitting ministers and dozens of former ministers, media reports say.
The detentions came hours after the new committee, headed by Crown Prince Mohammed bin Salman, was formed by royal decree.
Prince Alwaleed bin Talal, a billionaire with investments in Twitter and Apple, is among those held.
King Salman also replaced the heads of the national guard and the navy.
The royal decree setting up the committee declares: “The homeland will not exist unless corruption is uprooted and the corrupt are held accountable.”
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‘A shock to Saudis unused to change’
Analysis by Frank Gardner, BBC security correspondent
The events of Saturday night in Saudi Arabia are nothing short of seismic for that country. In a bold, pre-planned move, the 32-year old Crown Prince has removed the final obstacles to his gaining total control over the world’s richest oil producer and home to the holiest shrines in Islam.
Presented to the world as an anti-corruption drive, the arrests of princes, ministers and the billionaire tycoon Prince Alwaleed bin Talal have shocked Saudis unused to sudden change.
The crown prince is largely popular, especially amongst young Saudis, but many older, more conservative citizens think he is moving too far too fast. He has started an unwinnable war in Yemen while still fighting the extremists of so-called Islamic State. He has also backed a damaging boycott of Gulf neighbour Qatar.
But his supporters hail his efforts to modernise Saudi Arabia and, after decades of rule by old men, they welcome a fresh vision from a man who could well be king for the next 50 years.
The new anti-corruption committee has the power to issue arrest warrants and travel bans, the state-owned Saudi Press Agency (SPA) reported.
It is not clear on what grounds the detentions were made but Saudi broadcaster Al-Arabiya said fresh investigations had been launched into the 2009 Jeddah floods and the outbreak of the Mers virus which emerged in Saudi Arabia in 2012.
Other than that of Prince Alwaleed, the names of the detainees could not be confirmed immediately.
Shares in Kingdom Holding, the investment firm owned by the prince, plunged 9.9% in early trade on the Saudi stock market.
Kingdom Holding is one of the country’s most important investors. Apart from Twitter and Apple, it has shares in Rupert Murdoch’s News Corporation, Citigroup bank, the Four Seasons hotel chain and ride-sharing service Lyft.
Prince Alwaleed, who owns London’s Savoy hotel, is one of the richest men in the world, with a net worth of $17bn (£13bn) according to Forbes.
King Salman dismissed national guard minister Prince Miteb bin Abdullah and navy commander Admiral Abdullah bin Sultan bin Mohammed Al-Sultan, with no official explanation given.
Prince Miteb, son of the late King Abdullah, was once seen as a contender for the throne and was the last member of Abdullah’s branch of the family at the highest echelons of Saudi government.
Stronger power base
Madawi Al-Rasheed, who is a visiting professor at the London School of Economics’ Middle East Centre, told the BBC the purge gave Prince Mohammed control over the country’s security forces.
“It’s very difficult to see it as an anti-corruption move,” he said.
“This is really a purge that consolidates Mohammed bin Salman’s power base. He wants to remove the last remaining cousin who controls a paramilitary force that is very modern and also capable of challenging his rule. There are no more princes who can do that with a military or security base.”
Prince Mohammed recently said the return of “moderate Islam” was key to his plans to modernise Saudi Arabia.
Addressing an economic conference in Riyadh, he vowed to “eradicate the remnants of extremism very soon”.
Last year, Prince Mohammed unveiled a wide-ranging plan to bring social and economic change to the oil-dependent kingdom.