Israel's Antiquities Authority said on Monday the man was on a weekend dive in northern Israel when he spotted a trove of ancient artifacts that included anchors, pottery and a metre-long sword.

The diver was about 150 metres off the coast in five-metre-deep water when he made the discovery.

Experts say the area provided shelter for ancient ships and is home to many archaeological treasures, some dating back 4000 years. But such discoveries can be elusive because of the constantly shifting sands.

Fearing his discovery might be buried, the diver took the sword ashore and delivered it to government experts, the authority said. The weapon is estimated to be 900 years old.

"It was found encrusted with marine organisms, but is apparently made of iron," said Nir Distelfeld, an inspector in the authority's robbery prevention unit.

"It is exciting to encounter such a personal object, taking you 900 years back in time to a different era, with knights, armour and swords."

The sword is to be cleaned and further analysed, while the diver, identified as Shlomi Katzin, was given a certificate of appreciation for good citizenship.

Australian Associated Press