MANILA - The Supreme Court on Friday ousted Chief Justice Maria Lourdes Sereno, a court spokesman said, in an unprecedented move that analysts said could imperil democracy in the country.

Sereno, the first woman to hold the top post in the judiciary, had contested the validity of a "quo warranto" petition that led to her ouster, saying she could only be removed through ongoing impeachment proceedings.

The high court en banc voted 8-6 on Friday to grant the petition by Solicitor General Jose Calida and 9-5 in favor of the argument that it was the proper remedy.

Calida had cited Sereno's failure to fully disclose her wealth when she applied for the Supreme Court's top post in 2012. In another vote on Friday, 9 justices said quo warranto was the proper remedy to remove Sereno while 5 said it was not.

The order is effective immediately, Supreme Court spokesman Theodore Te said.

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Analysts said Sereno's ouster was a game-changer.

"Yung hinaharap dito is one of the breakdown of the rule of law, break down of checks and balances," Institute for Political and Economic Reform executive director Ramon Casiple told ABS-CBN News.

(What we are facing here is a breakdown of the rule of law, breakdown of checks and balances.)

"In effect, 'yung mga grupo na nasa Supreme Court presume themselves na nasa above all. 'Yun ang isang delikado kasi it can lead to anything, meaning there are no rules," he said.

(In effect, these groups in the Supreme Court presume themselves to be above all. That's dangerous because it can lead to anything, meaning there are no rules.)

The ruling sets a "very bad precedent" because such proceedings could now be used against "any and all public officials," said Lyceum College of Law Maria Soledad Derequito-Mawis.

The ruling would moot the impeachment case in Congress against the 57-year-old Sereno, who was appointed by former president Benigno Aquino III, the predecessor of incumbent President Rodrigo Duterte.

Sereno is the country's second chief magistrate to be removed from office under the 1987 Constitution. In 2012, the Senate sitting as an impeachment court ousted her predecessor, Renato Corona for failure to fully disclose his wealth.

Lawyer Lorenzo Gadon, who sought Sereno's impeachment, said before the decision: "It is quite unfair, unjust and illegal that she was considered the chief justice."

• Corona found guilty

It is, however, the first time in Philippine history that a chief justice would be removed through a quo warranto plea, a legal recourse Sereno's camp had argued as incorrect.

• Sereno: OSG guilty of forum shopping

In April, Duterte declared that he was Sereno's "enemy" after she questioned why the Solicitor General, who is under the President's office, wanted her out.

Duterte also ordered the House of Representatives to expedite her impeachment.

The President and the Chief Justice clashed soon after Duterte assumed office in 2016, after she said members of the judiciary who are included in the chief executive's "drug list" should be given due process.

• Duterte to Sereno: I am now your enemy

Calida's petition sought to nullify Sereno's appointment, saying she was "unlawfully holding" office due to her alleged failure to submit all her Statements of Assets Liabilities and Net worth (SALNs) when she applied for her post, as required by the rules.

• SolGen seeks nullification of Sereno's appointment

Sereno is expected to file a motion for reconsideration.

If the ruling is sustained on appeal, it would allow Duterte to appoint a new Chief Justice after candidates are vetted by the Judicial and Bar Council (JBC).

Sereno was supposed to stay in her post until her retirement at age 70 in 2030.