Italian energy giant ENI on Sunday announced the discovery of the "largest ever" offshore natural gas field in the Mediterranean inside Egypt's territorial waters.

The discovery, confirmed by Egypt's oil ministry, could hold a potential 30 trillion cubic feet (850 billion cubic metres) of lean gas in an area of about 100 square kilometres (40 square miles), it said in a statement.

The so-called Zohr project is "the largest gas discovery ever made in Egypt and in the Mediterranean Sea," it said, adding the find would meet Egypt's own natural gas demands for decades.

The discovery -- potentially one of the world's largest natural gas finds -- is located at a depth of 4,757 feet (1,450 metres) in the Shorouk Block, ENI said.

It said Eni's CEO, Claudio Descalzi, has visited Cairo and discuss the discovery with Egyptian leaders including President Abdel Fattah al-Sisi.

"This historic discovery will be able to transform the energy scenario of Egypt," Descalzi said in the statement.

The firm said it will "immediately appraise the field with the aim of accelerating a fast track development of the discovery".