The Foreign Office is warning visitors to Barcelona and other parts of Catalonia there could be more protests and violent clashes in the region.
Nearly 900 people were injured in clashes with police over the weekend, while they were trying to cast their votes in an independence referendum.
Four are seriously injured but stable, according to the Catalan health service.
Footage showed police firing rubber bullets, hitting voters with batons and dragging people away from polling booths.
The FCO said: "Demonstrations have taken place in Barcelona and other areas of the Catalonia region and may continue for some days.
"They may occur with little or no warning and even demonstrations intended to be peaceful can escalate and turn confrontational.
"You should exercise caution if you’re in the vicinity. Demonstrations may also cause some disruption and delays to transport services."
A general strike has been called across the Catalonia region in demonstration against the violence.
