A volcano under the sea erupted Saturday off Hierro, in the Spanish Canary Islands, the latest eruption in three months of seismic activity in the region, local officials said.

The eruption released gas and threw up fragments of smoking lava some 2.5 kilometres (1.5 miles) off the coast, said island officials, adding that scientists had identified it as an underwater eruption.

An eruption on Monday five kilometres off the coast was detected about a kilometre down in the sea.

On Wednesday, the surface of the sea off the island changed colour. Locals reported a strong smell of sulphur and found dead fish floating in the water.

The island of Hierro, which has about 10,000 inhabitants, has been on red alert, the highest level since a series of eruptions and tremors that began in July.

The last major volcanic eruption off the Canary Islands happened off Teneguia, Las Palmas, in 1971.