San Jose, Jan 7 - The Turrialba volcano in Costa Rica has become active for the first time in 40 years.

The authorities were on alert Wednesday, a day after the eruption of the 3,300-metre volcano located 80 km northeast of San Jose.

According to the Seismological Institute of the Central American country (Ovicori), the volcano spit clouds of "white powder". According to vulcanologists, it is not ash but an as yet unidentified matter.

Two villages on the mountainside were preventively evacuated, local media reported Wednesday. Experts regarded it as likely that there would be a bigger eruption.

Five villages on the Turrialba valley were covered in the powder, which mixed with rain to take on a darker colour.

The most recent eruption on the Turrialba dates back to 1863, when ash from the volvano drifted as far as Nicaragua. Its activity stopped altogether 40 years ago, making it possible to climb up to the top for some time.

The four volcanos in the central region of Costa Rica, which holds about half the country's 4.5 million people, include the Turrialba, the nearby Irazu, the Poas and the Barba.

Last year, the Poas - very close to San Jose - had a large eruption.

Further north lies the ever-active Arenal, whose eruption in 1969 killed about 90 people. (dpa)