Lascar is around 200km inland from the Chilean coastal city of Antofagasta, near the country’s northern borders with Bolivia and Argentina.
It is near San Pedro de Atacama, a popular destination for trekking the Atacama desert.
The eruption happened on Saturday (10 December), with Chile’s National Geology and Mining Service raising its alert level from green to yellow.
A 5km exclusion zone has been set up around the volcano’s crater. The Foreign Office hasn’t issued new travel advice.