Archaeologists working in northern Greece may have uncovered the tomb of Alexander the Great.

The celebrated king of the ancient Macedonian state is known as one of history's few "undefeatable" rulers. By the time of his death, aged 32 in 323BC, Alexander had conquered Egypt, Persia and Asia, building the largest empire the world had yet seen.

Archaeologists discovered what appeared to be a burial mound at a site in Amphipolis near the Macedonian city of Serres, about 600km north of Athens, local media reported.

The mound dates back to the end of the fourth century BC. Alexander died aged 32 in Babylon, ancient Mesopotamia (modern-day Iraq), under mysterious circumstances. The location of his grave remains unknown.

At 498m long and three metres high, the pyramid-shaped mound is widely thought to be a royal Macedonian grave as it has marble-faced walls and is ten times larger than the tomb of Alexander's father, Philip II of Macedon.

Archaeologists also believe that an Amphipolis lion statue, a symbol of ancient Macedonia, was placed on top of the mound but time and perhaps unfriendly hands have destroyed it.

Lead archaeologist Aikaterini Peristeri said the grave could contain a "significant individual" or individuals, hinting at the possibility that the remains of Alexander and his wife Roxanne, as well as his young successor, are inside the tomb.

However, the Greek Ministry of Culture cautioned that though the archaeological find was "very remarkable", it would be "overbold" to state that it is the tomb of Alexander the Great until the excavation is complete.

"The finding of Amphipolis is certainly very important, but before the excavation proceeds, any interpretation and mainly any identification with historical figures is too risky," the ministry said.

According to the General Directorate of Antiquities and Cultural Heritage of Greece, excavations at Amphipolis began in the 1960s. Recent work uncovered the mound inside a circular enclosure. Excavation work on the tomb has now been prioritised.