Thousands of residents of Spain's La Palma island have been ordered to stay at home due to "extremely adverse" air quality generated by the Cumbre Vieja volcano that has smouldered for almost three months.

The eruption, which has sent spectacular rivers of molten lava running down the slopes of Cumbre Vieja since 19 September is the longest running on the Spanish Canary island since records began in 1500.

Around 24,500 residents in Los Llanos de Aridane, El Pasoand Tazacorte - a third of La Palma's inhabitants - were asked to stay indoors due to emissions of sulphur dioxide that have reached toxic levels, authorities said.

Emergency services instructed residents to shut their windows and turn off air conditioning units to avoid inhaling toxic fumes.

They also recommended postponing outdoor activities and advised people to wear a heavy-duty mask if they had to venture out.

Houses covered with lava following the volcano eruption

In affected municipalities, students were told to remain in schools and parents not to pick them up until the air quality clears.

Lava flows have damaged or destroyed at least 2,910 buildings, according to the EU satellite monitoring system Copernicus, forcing the evacuation of thousands of people from their homes on the island, part of the subtropical Canaries archipelago.