A large metallic ball has fallen out of the sky on a remote grassland in Namibia, prompting baffled authorities to contact NASA and the European space agency.

The hollow ball with a circumference of 1.1 metres was found near a village in the north of the country some 750km from the capital, Windhoek, according to police forensics director Paul Ludik.

Mystery "space ball" ... baffled authorities have contacted NASA and the European space agency.

Locals had heard several small explosions a few days beforehand, he said.

With a diameter of 35cm, the ball has a rough surface and appears to consist of "two halves welded together".