Costa Rica's Arenal volcano has erupted, spewing geysers of lava, ash and toxic gases from its crater and forcing the evacuation of the national park where it is located.

The 1633-metre-tall cone-shaped mountain in northern Costa Rica shuddered into activity at 4am this morning issuing eight successive rivers of lava that flowed down its steep slopes, National Volcanology and Seismology Observatory expert Elicer Duarte said.

He said nobody was at risk from the eruptions but authorities as a precaution evacuated the Arenal National Park, 80km north-east of San Jose.

The Arenal Volcano is one of Costa Rica's major tourist attractions and the park has scores of hotels, restaurants, nightclubs and shopping centres.

No estimates were given of how many people were inside the park when the eruption began.

Arenal's last major eruption in July 1968 killed 89 people. Smaller eruptions have occurred at least six times over the past 35 years.

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