Costa Rica's Turrialba volcano staged its most powerful eruption in years overnight, belching a plume of gas and ash that was reported to sprinkle the capital San Jose some 50 km (30 miles) away, emergency services said on Thursday.
Some people were being evacuated from the surrounding area as a precaution, but there were no reports of damage or injuries.
Television footage showed ash falling like snow against the night sky onto the backs of cows.
"We saw fiery explosions. We must confirm whether it was lava or burning material that fell so spectacularly," Raul Mora, a volcano expert with the National Seismological Network, told local television, adding the volcano was highly active.
The last time Turrialba spewed lava was around 1863, Mora said.
The national park around the volcano has been closed since 2010, when it also spewed ash, as a precautionary measure, according to the emergency services.
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