Some 1.5 million people have been taking part in Catalonia's annual independence rally in Barcelona, according to police.
Tens of thousands of people poured into the city waving the region's independence flag and brandishing the colours red and yellow.
This year's march aimed to be the biggest ever - and a protest against the Spanish government's tax laws.
Catalonia wants Madrid to review its tax agreement and provide a bailout.
The size of the turnout for the rally, which is held annually on 11 September to mark the Siege of Barcelona 300 years ago, forced organisers to change its route.
Alfred Bosch, an MP from the Republican left of Catalonia, told the BBC: "All the flags I can see are the pro-independence flags of Catalonia with the lonely star right in the middle of the triangle.
"And everybody is wearing these flags. I have never seen so many pro-independence flags in my all life."
Protester Teresa Cabanes told Reuters: "This is a blow for the government. People like me came from everywhere. I don't think they were expecting something as big."
The huge volume of people overwhelmed the mobile phone network, which shut down for hours as a result, reports say.