A pyramid of steaming black rock has emerged from the Atlantic Ocean off Spain’s La Palma as lava from the Cumbre Vieja volcano crashed into the sea, sending up plumes of white steam.

Despite fears of toxic gases, authorities say the air inland remains fine to breathe.

Lava from the volcano that began erupting 10 days ago reached the ocean just before midnight on Tuesday near the town of Tazacorte and began accumulating at the foot of a cliff until a cone of debris appeared above the waterline.

“It is now generating a structure that we call a ‘lava delta’ that is … extending the island to the west,” said Juan-Tomas Vazquez, a marine geologist aboard the Ramon Margalef research vessel, just offshore from the cliffside.

Eugenio Fraile, an oceanographer in charge of the research mission, told a videoconference the steam posed no risk for now but stressed the importance of the monitoring effort.

Thousands have been evacuated from their homes since the volcano erupted on September 19 and lava has engulfed nearly 530 houses and several banana plantations.

Spain has classified La Palma a disaster zone in a move that will provide financial support for the island.

Three coastal villages were locked down as authorities feared possible explosions and clouds of toxic gas as the lava hit the sea.

Tazacorte Mayor Juan Miguel Rodriguez Acosta told TV3 television that everyone in a two-kilometre radius had left the area.

Although La Palma’s council said the air remained “perfectly breathable”, residents would not be able to leave their houses for some time.

Local airline Binter said flights to and from La Palma had restarted on Wednesday after they were cancelled last week.

-AAP