Some of Europe's most spectacular prehistoric cave paintings have reopened to a handful of visitors at Altamira in northern Spain after a 12-year closure.

Renowned for vivid paintings of bison and animal-headed humans, the cave closed in 2002 because scientists said the breath from crowds of visitors was damaging the prehistoric art.

It has now been reopened to small, select groups of visitors who will have to wear masks and overalls while experts assess the impact on the paintings, Spain's culture ministry said.

A highlight of the art is a set of 14,000-year-old paintings of red and yellow bison plus horses, deer, humans with the heads of animals and mysterious symbols.

UNESCO listed the paintings as a World Heritage Site in 1985, as "masterpieces of creative genius and as humanity's earliest accomplished art".

The cave, whose walls are covered with paintings over more than 270 metres, was discovered in 1868 at Santillana del Mar, in the Cantabria region.

Experts say the cave was inhabited approximately 35,000 to 13,000 years ago.

The paintings are "exceptional testimonies to a cultural tradition and... outstanding illustrations of a significant stage in human history", UNESCO says in its listing.

The techniques of the paintings and realistic animal details mark "one of the key moments of the history of art", it says.

During the closure, visitors have had to look at a nearby replica of the paintings and only experts have been allowed into the cave.

In January, the foundation which manages the cave said it could reopen but only to groups of five people a week, and for just 37 minutes at a time.

The culture ministry said a first group of five, selected at random from visitors to a nearby museum, would be allowed into the cave today.

Overall 192 visitors will be allowed in by August, when experts will reassess the impact of the visits on the paintings.

"The aim is to analyse the impact of human presence on the conservation of the cave... to determine if continued access to the cave is possible or not," said junior culture minister Josa Maria Lassalle last month.