Costa Rica declared a state of emergency Thursday after eruptions of ash from a volcano forced international flights to be postponed and threatened the capital, authorities said.

"For several days now volcano Turrialba has had continual eruptions marked by the constant expulsion of ash," the National Emergencies Commission (CNE) said in a statement.

It declared a state of emergency for the capital San Jose and other central cities.

San Jose lies 36 kilometers (22 miles) from the volcano, which soars 3,432 meters (11,260 feet) above sea level.

Columns of ash from Turrialba have been blown by the wind towards San Jose and other towns such as Heredia, Cartago and Alajuela, home to an international airport.

Authorities said some international flights were suspended on Wednesday but air traffic returned to normal on Thursday.

The Seismological and Vulcanological Observatory at Costa Rica University said a seismic tremor was detected that was growing in intensity.

The CNE advised people to wear protective goggles, hats and special protective clothing outside.

It told them to carefully wash vegetables picked in the area.