A mysterious temple has been discovered among the ruins of an ancient sunken city described as the "Egyptian Atlantis".

Heracleion off Egypt's north coast slumped into the sea some 1,200 years ago and was lost for centuries until divers stumbled upon what's left of it in 2000, The Sun reports.

Studies of its sprawling ruins have been ongoing ever since, though we still don't know much about the once-great port town.

Now archaeologists have announced a series of astonishing new finds at the underwater site.

They've uncovered the remains of a Greek temple, as well as several boats brimming with treasures like coins and jewellery.

Ancient columns, 2,000-year-old pottery and bronze coins from the reign of King Ptolemy II (283 to 246 BC) were also found.

Heracleion is mentioned in a smattering of ancient texts, but was thought to be the stuff of legend for well over a millennium.

Sitting at the entrance to the Nile river, the city was said to be Egypt's main international trading port, sporting towering statues, enormous temples and a maze of bustling canals.

In one of history's greatest archaeological finds, a French scientist rediscovered the sunken city in the 1990s.

Buried under centuries of Nile silt, many of the ruins and artefacts dragged from its murky depths remain perfectly preserved thousands of years later.

Underwater archaeologists used a high-tech scanning device to uncover new parts of the ancient settlements, Egypt's Ministry of Antiquities reported this week.

Sections of the city's main temple were revealed, as well as a handful of new ports, helping the team to expand its ever-growing map of the ancient city.