There is no prospect of the volcanic eruption in Spain's Canary Islands ending "in the short or medium-term", experts said Wednesday after three-and-a-half weeks of activity.

At the Cumbre Vieja volcano on La Palma island, "levels of sulphur dioxide don't currently lead us to think the end of the eruption will be in the short or medium term," said Maria Jose Blanco, spokesman for the Canaries' volcanologist group Pevolca.

Other experts have suggested the event could last for weeks or even months.

Beginning on September 19, the latest eruption is the third in a century for La Palma, an island of 85,000 people, after San Juan in 1949 and Teneguia in 1971.

"The volcano's activity is not stopping and it doesn't seem that we can expect to observe a reduction in the coming days," Prime Minister Pedro Sanchez said Wednesday, during his fourth visit to the island since the eruption.

So far no-one has been killed by the continuous lava flows, but the molten rock has covered around 640 hectares (1,600 acres) and destroyed 1,400 buildings, 764 of them homes, Pevolca technical director Miguel Angel Morcuende said.

More than 6,000 people have been evacuated, hundreds of them leaving all their belongings to the lava.

Flights are currently reaching La Palma's airport, which has been closed twice during the eruption due to volcanic ash.

Weather forecasts suggest it will be able to remain open for at least the next four days.