Cairo - Archaeologists in Egypt discovered a "perfectly preserved" mummy inside a 2,600-year-old lime sarcophagus north of Cairo on Wednesday, Egypt's antiquities authority said.

Scientists said they believed the mummy, one of 30 discovered in a previously forgotten tomb near the step pyramid of Saqqara, could have been a nobleman from the time of the 26th Dynasty.

The 26th Dynasty ruled ancient Egypt from approximately 685 BC until Cambyses II of Persia sacked Memphis in 525 BC.

"Opening this sealed sarcophagus is a very important moment, especially because we are looking into the unknown - we do not know what we will find," Zahi Hawass, head of the Supreme Council of Antiquities, said in a statement.

Hawass and his assistant Abdel-Hakim Karara are leading a project to excavate a massive burial site at the foot of the Saqqara pyramid, 20 kilometres south of Cairo. Egypt's antiquities department says it believes only 30 per cent of the site's monuments have been uncovered.

The archaeologists said they believed ancient Egyptians had broken the lid of the sarcophagus when they buried it thousands of years ago, and that they had then restored it with mortar.

Thirty mummies, including four complete human mummies and a mummified dog, were found in the same 11-metre-deep tomb. A coffin for a small child was also found buried in the tomb.

The archaeologists said they also found a wooden coffin, but its lid was too decayed to open without the risk of causing it to crumble. (dpa)