Seismic activity has declined, with two tremors of a magnitude of around 2.5 recorded every hour on Tuesday, compared with several hundred of a magnitude of four or five in the hours preceding the initial June 4 eruption.

But Chile's National Service of Geology and Mining, which monitors volcanic activity, said the volcano had to be kept on red alert because of the possibility of another explosion.

Geologists said a "cork" of lava, which emerged on Tuesday and was blocking even more lava from spewing forth, had the potential to create a huge build-up in pressure.

AFP