The Canary Islands government warned on Tuesday that seismic activity in El Hierro was pointing to the risk of another volcanic eruption on the island.
The National Geographic Institute detected 31 tremors in the early hours of Tuesday, the biggest of which measured 3.9 on the Richter scale in the north of the island close to Frontera, where some 4,000 people live. Tremors were also felt on Sunday.
A volcanic eruption occurred in the sea south of the island on October 11, producing a sulfurous slick that was larger than the island itself.
"The scenario of a possible volcanic eruption cannot be ruled out from the new seismic activity that is taking place in the north," the government said.
The statement also warned islanders against eating fish until tests had been carried out for possible contamination.