A huge undiscovered “void", the size of a jet plane, has been found inside the Great Pyramid of Egypt.
The 30-meter-long secret chamber, sealed off 4,500 years ago, has remained untouched until this day, scientists revealed on Thursday.
The discovery, named simply "Big Void", has been confirmed using different technologies.
It is one of four spaces -- the king and queen's chambers and "Grand Gallery" -- now known to exist inside the Great Pyramid constructed under the auspices of Pharaoh Khufu.
"It is big," said co-discoverer Mehdi Tayoubi of the ScanPyramids project, whose group has been scanning through Khufu's pyramid since October 2015 using non-invasive technology.
"It's the size of a 200-seater airplane, in the heart of the pyramid," Tayoubi told AFP of the discovery, published in science journal Nature.
"There have been many theories about the existence of secret chambers inside the pyramid, but none have predicted anything this big," he said.
The pharaohs of ancient Egypt built the pyramids to hold their embalmed mummies, and stocked in them everything they thought would be required in their afterlife, including food, clothing and jewels.
The chambers of Khufu's pyramid had been plundered long before it was visited by modern archaeologists, and no relics remain from any of them.
"While there is currently no information about the role of this void, these findings show how modern particle physics can shed new light on the world's archaeological heritage," the authors wrote in Nature.
The team is already turning its attention to new technology for the next step -- possibly a miniature robot that can travel through tiny holes to examine the inside of the void without disturbing anything.
The void is the first major structure found inside the Great Pyramid since the 19th century, the research team said.
Khufu's pyramid, which is 139 meters high today, and 230 meters wide, is located in the Giza complex on Cairo's outskirts alongside smaller pyramids for kings Menkaure and Khafre and the Great Sphinx.
The massive pyramid, which is one of the largest structures ever built on Earth, was erected as a tomb for Khufu, also known as Cheops. Until this day, nobody knows for sure how it was built.
It is the oldest and only surviving construction among the Seven Wonders of the Ancient World.
The other wonders were the Colossus of Rhodes, the Hanging Gardens of Babylon, the Lighthouse of Alexandria, the Mausoleum at Halicarnassus, the Statue of Zeus at Olympia and the Temple of Artemis at Ephesus.