Ash coated buildings and vehicles in San Jose, 30km (19 miles)
from the Turrialba volcano.
Residents
reported that the air reeked of sulphur.
TV footage
showed shuttered schools and hundreds of people flocking to hospitals with
breathing and skin problems.
The National
Emergencies Commission advised people to wear masks and tight clothing to
protect their lungs and skin from the ash.
"It seems to me to be the strongest (Turrialba) eruption in
the past six years," volcanologist Gino Gonzalez said.
He spoke to
media near the site of Friday's eruption, where a large cloud of grey smoke was
billowing from the 3,340m (11,000ft) volcano.
Mr Gonzalez said
the wind was blowing the ash and smoke westward, toward the country's most
populated areas.
