Six Catalan separatists serving long jail terms for a failed 2017 independence bid were let out on Tuesday to testify at a hearing in the regional parliament.

It was the first time the jailed separatists had appeared in public since their conviction in October, and on arrival at the parliament in Barcelona, they were greeted by dozens of supporters who broke into applause, shouting "freedom".

Among those attending the hearing was former vice-president Oriol Junqueras who, as the main defendant, is serving a 13-year sentence after his boss, former president Carles Puigdemont, fled to Belgium to avoid prosecution.

The sentencing of nine Catalan separatist leaders sparked a wave of mass protests across this wealthy northeastern region of Spain, some of which turned violent. They were brought to parliament in unmarked cars, their appearance in the chamber closely watched by a discrete clutch of police in civilian clothing, an AFP correspondent said.

Their presence was requested by the region's separatist government, which enjoys broad powers, particularly in prison administration. It authorised them to appear at a hearing on Madrid's temporary imposition of direct rule in Catalonia following the 2017 separatist crisis. Their appearance comes following a confrontation between the two main separatist parties that make up Catalonia's ruling coalition, Puigdemont's JxC (Together for Catalonia) and Junqueras' ERC (Republican Left of Catalonia).

Tensions came to a head Monday after current Catalan president Quim Torra lost his status as a regional lawmaker over his conviction last month for "disobedience". Despite him appealing, the electoral commission ordered the parliament to implement his suspension immediately.

JxC decided to ignore it and asked the ERC to do the same -- but it refused, saying ignoring the ruling would render all decisions in which Torra cast a vote null and void, effectively paralysing parliament. The two parties are also at loggerheads over the key role the ERC played in facilitating the return to power of Spain's Socialist Prime Minister Pedro Sanchez in exchange for talks over the "political conflict".

"Nobody is more pro-independence than me," Junqueras said in his first appearance in the chamber since October 2017, when the separatist government held a banned secession referendum then issued a short-lived independence declaration, sparking Spain's worst political crisis in decades. "In the same way that we are champions of the republican cause, we are also champions of dialogue."

He also said they wouldn't hesitate to hold another referendum. "A referendum on self-determination is a normal thing and we want to do it again. And we will do it again," he said.