Spain on Monday ordered more than 30,000 people to remain indoors on La Palma island because of toxic gases from a volcano that has been erupting for months.

After several days of low-level activity, the Cumbre Viejo suddenly sprang to life on Sunday with several explosions sending a vast cloud of ash and smoke into the sky.

The regional government of the Canary Islands, which lie off Africa's northwest coast, ordered residents of three municipalities to lockdown owing to high levels of sulphur dioxide in the air.

The three municipalities are home to roughly 33,000 people, or 38 percent of the population of the island, according to national statistics institute INE.

"Close the doors, windows, shutters and prevent any air coming in from the outside," the regional government said in a statement.

"Confine yourself, if possible, in the rooms located furthest inside."

The authorities also recommended that people turn off air conditioning and heating and use tape to seal doors and windows.

"If you find yourself outside, be aware that a car is not a safe place and confine yourself to the first building you find," the statement said.

More than 7,000 people have been evacuated from their homes since the volcano erupted on September 19, spewing out rivers of lava that have slowly crept towards the sea.

Nobody has died as a result of the eruptions, but more than 2,800 buildings have been destroyed, according to EU monitoring service Copernicus.

This is La Palma's longest eruption and the third in a century, with previous ones in 1949 and 1971.