Thousands of far-right supporters protest against the government in Madrid

Tens of thousands of supporters from Spain's far-right Vox party demonstrated nationwide to protest Prime Minister Pedro Sanchez's leftist government.

Police said 25,000 people gathered in central Madrid's Colon Square, where protesters unfurled flags and called on Sanchez to go, while demonstrations also took place in cities across Spain.

Vox leader Santiago Abascal denounced a "government of treason, insecurity and ruin" after recent changes to the criminal code and the approval of a new law against sexual violence.

He lambasted the planned abolition of the crime of sedition, of which nine separatist leaders were convicted over their role in the Catalonia region's abortive secession bid in 2017. An offence carrying a lower prison sentence will replace it.

"We have a government that governs against the people, lowers prison sentences for crimes, disarms the police," Abascal told his followers in the Spanish capital.

The right believes the modified criminal code, which should be in place by the end of the year, will encourage further attempts to separate the northeastern Catalonia region from Spain.

Abascal said sexual assaults had doubled since Socialist premier Sanchez took power in 2018 and denounced a law he claimed allowed rapists and paedophiles to leave prison earlier.

He was referring to a flagship government law against sexual violence that toughened penalties for rape but eased sentences for other sexual crimes, setting some convicts free after their jail terms were reduced.