An 11-year-old boy and his parents have died after falling into a volcanic crater in Italy while the family's seven-year-old son looked on.

Police said the 11-year-old's parents tried to rescue him after he wandered off the path at the Solfatara Crater near Naples, and slipped.

They added that it was not immediately clear if the family had been killed by gases or an explosion of super-heated mud.

The Italian family's seven-year-old son remained outside the prohibited area while his parents attempted to rescue his brother.

The crater is in the Phlegraen Fields, a sprawling constellation of ancient volcanic craters popular with tourists.

Just a few inches below the surface, the fields are scorching hot.

Heavy rain in recent days may have played a role in the deaths by creating more openings in the volcanic field's surface.

Signs around the crater in multiple languages warn of the danger of burning from high soil temperatures and steam up to 160C (320F).

Visitors are told to stay clear of fumaroles, openings in the Earth's crust that emit steam and gases, and not to climb the slopes or breach the fences.