MADRID (Reuters) - Authorities on the Spanish Canary Island of La Palma have warned that a sudden increase in seismic activity could herald a volcanic eruption in the coming days or weeks.
Spain's National Geographic Institute has detected 4,222 tremors in a so-called "earthquake swarm" in the Cumbre Vieja national park, around the Teneguia volcano in the far south of the island.
As the quakes intensified and moved closer to the surface, the Canary Island's regional government on Tuesday put the island on a yellow alert for an eruption, the second of a four-level alert system.
It said on Thursday there was no clear evidence for an immediate eruption, though warned the situation could evolve rapidly.
"More intense earthquakes are expected in the coming days," it said in a statement.
More than 11 million cubic metres (388 million cubic feet)of magma have seeped into Cumbre Vieja in recent days, swelling the peak by around 6 centimetres, the Volcanic Institute of the Canaries said on Thursday.
Rising sharply out of the Atlantic around 100 kilometres to the west of southern Morocco, the Canary Islands are home to Spain's most active and best known volcanoes, including Teide in Tenerife and Timanfaya in Lanzarote.
Teneguia last erupted in 1971 - the last surface eruption to occur in Spain - while a volcano off the tiny island of El Hierro erupted underwater in 2011.