Catalonia's vice-president yesterday admitted that plans to hold an outlawed independence referendum had been dealt a major blow by a crackdown the previous day, as people gathered in Barcelona for a second day of protests.

Thousands took to the streets of the Mediterranean seaside city on Wednesday after police detained key members of the team organising the vote slated for October 1 in a region deeply divided over independence.

Authorities seized nearly 10 million ballots destined for the vote, seriously damaging separatist plans for a referendum with a semblance of legitimacy, even if it was never going to be recognised by Madrid or abroad.

After a day-long protest that lasted well into the night, several thousand independence supporters gathered again yesterday in front of the high court in what influential separatist organisations said would be a "permanent mobilisation" until the officials are freed.

Oriol Junqueras, the region's vice-president whose deputy was among those arrested, told Catalonia's TV3 television that the operation meant "the rules of the game have been changed."

"The circumstances today are different because a significant part of our team, half of the economics team, has been arrested," he said.