Britons in Barcelona have been urged to stay indoors and avoid Las Ramblas after the terror attack in which a van crashed into people, killing 13 people.
The van drove in to people at around 5pm local time, injuring 50 people. Police have arrested a man in connection with the incident.
Witnesses reported screams and panic after it happened and people fled the scene.
The Foreign Office has updated its travel advice for those in Barcelona as the situation develops.
“The British Embassy in Madrid and Consulate General in Barcelona are in contact with local authorities and urgently seeking further information following reports of an incident in central Barcelona.
“Local authorities have advised people to stay inside and stay away from the Las Ramblas area of the city.
“If you’re in the immediate area you should take care and follow the advice of the local security authorities; press reports suggest that some public transport, particularly the metro, has been affected; this page will be updated as the situation develops.”
A Foreign Office spokesperson said: “We are in contact with the Spanish authorities and seeking more information following an incident in Barcelona.
“Anyone in the area should follow the advice of the emergency services.”
Theresa May has said her thoughts are with the victims of the “terrible attack” in Barcelona, adding: “The UK stands with Spain against terror.”
The attack bears similarities to attacks in London at Westminster Bridge and London Bridge, which both involved vehicles driving into pedestrians.
Sadiq Khan tweeted: “London stands with Barcelona against the evil of terrorism.”
Boris Johnson tweeted they were “doing all we can to identify whether Brits need help”.