Riot police were deployed to prevent any demonstrators from entering the court building.

In a social media post, the Constitutional Court wrote that the two judges the government wants to prosecute were still the legally appointed senior justices of the court.

"All persons participating in these actions are committing the crime of a coup d'etat," it said.

In a social media post, Tusk wrote: "Restoring the rule of law is our duty. After years of Law and Justice's lawlessness, this is a difficult, sometimes painful process that requires decisive action. There is no other way."

President Karol Nawrocki, who is backed by PiS, ordered his plane be turned back to Warsaw on his way to Senegal to attend the Summer Youth Olympic Games.

The PiS-led government took office in 2015 and moved swiftly to appoint judges to the court to gain a majority there because the court has the power to decide on the legality of legislation.

Leading European courts - the European Court of Human Rights and the Court of Justice of the European Union - subsequently ruled the PiS majority had elected three of the judges improperly because they were duplicating positions that had been validly filled by the previous parliament.

The European courts ruled Poland's Constitutional Court was no longer an "independent and impartial tribunal", and Tusk's government has used those rulings as a basis to stop publishing the tribunal's rulings.

Tusk has failed to undo the PiS-era changes, partially because Nawrocki and his PiS-backed predecessor Andrzej Duda used their presidential vetoes to block his attempts.

Nawrocki has also refused to swear in five Constitutional Court judges elected by parliament since March on the grounds of alleged flaws in their selection procedure.

One of those judges, Anna Korwin-Piotrowska, has now been placed in temporary charge of the court.