"The alert level is rising from green to yellow," Vanessa Rosales, the head of the National Emergency Commission, told a news conference in the capital San Jose, some 40 kilometers (25 miles) from the volcano.

Winds were sweeping some ash toward the capital, Rosales said, adding that "intense but low" seismic activity continued in the crater area.

Evacuations would extend from a three-kilometer radius to five or six kilometers, with some 50 people already evacuated, she added.

The 3,328-meter (10,918-foot) volcano erupted Tuesday, spewing ash and rocks and forcing 21 people in its vicinity to evacuate their homes.

The last major eruption of the Turrialba volcano was in 1856. It has had at least five major explosive eruptions in the last 3,500 years.

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