All access to the volcano has been closed after the The Piton de la Fournaise Observatory detected a "seismic crisis" starting at around 4:47 am (0047 GMT), the island's prefecture said on X.

"This indicates that magma is leaving the magmatic reservoir and propagating toward the surface," the observatory said in a statement on Thursday.

The prefecture declared an Alert Level 1, warning on X that an eruption is "probable or imminent".

It also ordered the closure of the volcano's caldera as of 6:00 am, January 1.

The Piton de la Fournaise, situated in an uninhabited area in the southeast of the island, has erupted around 20 times over the last decade, and its violent bursts of activity often prompt stunning lava flows.