BARCELONA -- There are a "number of deaths" and "many injuries" after a van rammed into a crowd of people in the heart of Barcelona, a Catalan police spokesman told CNN.
The spokesman earlier said the incident Thursday afternoon was "most likely" a terror attack.
Catalan police tweeted that they had activated their terror response protocols, but could not confirm the motive for the incident.
It occurred near the popular tourist area of Las Ramblas, which has been sealed off, according to a police spokesman.
Catalan police told everyone in the vicinity of Plaça de Catalunya to remain inside.
Reuters reported that local emergency services have requested the closure of metro and train stations in the vicinity of the incident. Police told people to avoid the area.
Catalan police tweeted that the search for the perpetrator of what they called a "massive trampling" was still ongoing as of 6 p.m. local time (12 p.m. E.T.)
Police also asked people to stay away from the area.
A witness told local media the situation was "very tense" and that all surrounding shops were being evacuated.
The witness said at least eight ambulances were at the scene. Emergency services said the area had been cordoned off and all public transportation stopped.
A witness who is hiding in a shop nearby heard gun shots, according to local media outlet TVE24. Another witness said he saw a van driving "around 80 kilometers" per hour, or 50 mph. He said "there is no doubt it was intentional," according to TVE24.
Spanish Prime Minister Mariano Rajoy tweeted: "In contact with all administrations. Priority: tend to the injured in Las Ramblas and facilitate the work of security forces."
The US Consulate in Barcelona posted on Twitter: "We are aware of a reported incident at Las Ramblas in Barcelona. Please avoid the area and monitor local police @mossos for updates."
Las Ramblas is a predominantly pedestrianized street popular among tourists in Barcelona. Located in the center of the city, the tree-lined street is especially crowded in the summer, the height of tourist season.
The promenade passes by kiosks, flower sellers, pavement cafes and bars. It includes a number of the city's most popular sites.
Barcelona is consistently ranked one of the world's most visited cities.
Developing story - more to come
(CNN's Vasco Cotovio, Claudia Rebaza, Julia Jones and Tamara Qiblawi contributed to this report.)
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