Barcelona has been plunged into lockdown by Spanish police after controversial Catalan separatist Carles Puigdemont returned to the region's capital despite an arrest warrant - and then promptly vanished.

Puigdemont had addressed legions of followers just outside the Catalan parliament to revive support for his cause after his failed illegal independence attempt in 2017.

After returning from his self-imposed exile in Belgium, he triumphantly announced: "They thought they'd be celebrating my arrest and they thought that this punishment would dissuade us, and you... Well, they are wrong."

A loudspeaker announcement called on the crowd to accompany Puigdemont in a march towards the Catalan parliament.

But while senior officials of Puigdemont's Junts party and members of the moderate separatist Esquerra Republicana de Catalunya made their way to the building, he disappeared backstage.

After vanishing, neither journalists nor police were able to find Puigdemont - and his departure sparked chaos as they attempted to hunt him down.

The search for the separatist caused traffic jams across Barcelona, as well as near the border with France, as police set up roadblocks and searched car boots suspected of harbouring him.

The 61-year-old firebrand faces an arrest warrant in Spain for alleged embezzlement, which he denies.

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In response to his brief appearance, the Catalan Mossos d'Esquadra police force have activated Operation Cage - but officials fear Puigdemont has slipped the net once again.

And it later emerged that he got into a white car belonging to none other than a Mossos d'Esquadra officer, a Catalan government source said.

A spokesperson for the regional police said one of its officers had been arrested "as part of the investigation into Puigdemont's whereabouts."

Just yesterday, he announced he had started his "return trip from exile", saying he remained committed to attending Thursday's regional parliament session, in which lawmakers are sitting to swear in the region's new leader following an election in May where Junts finished second.

And if police do manage to track him down, his arrest could jeopardise the national government's fragile alliance with Junts - short for Junts per Catalunya, or Together for Catalonia - on which it relies for legislative support.

Spain's PM Pedro Sanchez had granted Puigdemont and his followers amnesty in return for Junts's seven votes in the national parliament, which were crucial in returning him to power after last year's general election returned a hung parliament.

The Spanish Supreme Court had rejected any such amnesty and ordered that a warrant for his arrest be kept active, stipulating that the amnesty does not extend to the crime of embezzlement of public funds.

Puigdemont reacted by comparing the court to the Sicilian Cosa Nostra mafia, calling lawmakers "Toga nostra" - a wordplay on the judges' gowns.