La Cumbre Vieja volcano began erupting on September 19th, forcing 6,000 people from their homes as the lava scorched its way across 600 hectares (1,400 acres) of land.
Miguel Angel Morcuende, head of the cell handling the crisis, told journalists Monday that part of the cement factory had gone up in flames.
“Consequently, and until we can analyse if the air quality allows for normal life, we have decided to lockdown,” he added.
The order concerns between 2,500 and 3,000 people living near the cement works on the west of the island in the Canaries archipelago, he said.
On Saturday, part of the volcano’s cone collapsed, sending new rivers of lava pouring down the slopes towards an industrial zone.
Flights to the island resumed on Saturday after two days on hold because of the ash blasted from the volcano.
Despite the damage from the eruption – more than 1,200 buildings have been destroyed, say local officials – no one has so far been killed or injured in the disaster.
This is the third volcanic eruption on La Palma Island, home to 85,000 people, in a century, although the last one dates back to 1971.