Crawl through a labyrinth of narrow tunnels in near total darkness and suddenly they appear: two great winged bulls dating from the Assyrian empire found intact under the ground of Mosul.

But as fighting rages to evict the Islamic State (IS) group from the main city in northern Iraq, it will be a race against time to save the archaeological treasures uncovered in the tunnels.

The jihadists dug the network of tunnels to plunder artefacts under a hill reputedly housing the tomb of the Prophet Jonah, the Nabi Yunus shrine which they dynamited in July 2014.

"We fear it could all collapse at any time," entombing the treasures, said Layla Salih who is in charge of antiquities for Nineveh province.

"There are cave-ins in the tunnels every day."

Iraqi authorities discovered the underground labyrinth, from which IS plundered to sell on the black market, after they recaptured east Mosul at the end of January.

Miraculously, several choice pieces survived the looting and appear as the crouched visitor winds through the maze of tunnels with its scent of damp clay.

A member of the Iraqi troops stands next to archeological findings inside an underground tunnel in east Mosul. (ARIS MESSINIS / AFP)

Salih said the artefacts date back to the eighth century BC in the Assyrian period and hail from the palace of King Esarhaddon whose existence in the area was known to Iraqi archaeologists.

Two mural sculptures in white marble show the winged bulls with only the sides and feet showing.

The tunnels lead to bas-reliefs with inscriptions in cuneiform alphabet and two mural sculptures of four women's faces from the front.

"These finds are very important. They teach us more about Assyrian art. In general, their sculptures show people in profile, whereas here we have women face on," said Salih.

The impressive maze of tunnels dug by the jihadists to carry out archaeological excavations is located in the heart of the hill that houses the tomb of the Prophet Jonah. (ARIS MESSINIS / AFP)

She said IS had not been able to extract many of the treasures for fear of the hill collapsing altogether but other removable artifacts, especially pottery, were certainly plundered.

Iraqi authorities found 107 items of pottery in a house east of Mosul that were in good condition and most likely exhumed from the tunnels of Nabi Yunus.

- Picture of desolation -

After their capture of swathes of Iraqi territory to the north and west of Baghdad in 2014, the jihadists carried out a widespread campaign of destruction of archaeological and religious sites.

Many shocking scenes were filmed and posted on the internet, such as the destruction of Nimrud, jewel of the Assyrian empire founded in the 13th century BC, with a bulldozer, pickaxes and explosives.

The hilltop of Nabi Yunus is a picture of desolation, the once elegant Jonah's tomb reduced to a ruin of smashed and twisted columns.

In the Mosul region alone, "at least 66 archaeological sites have been destroyed, some of them transformed into parking lots. Muslim and Christian places of worship have suffered massive destruction, thousands of manuscripts have disappeared", Iraq's Deputy Culture Minister Qais Rashid told a UNESCO-organised conference in Paris last month.

Salim Khalaf, a ministry official, said at the forum that more than 700 archaeological items had been exhumed from the tunnels of Nabi Yunus and sold on the black market.

The priority at the site is to carry out studies on how to stabilise the tunnels and save the hill from collapse, explained Salih.

"The security situation in the eastern sector of Mosul is still unstable. There's fear of (IS) drones and terrorist attacks," she said. "We need foreign expertise, but to have that, security must be improved."

As if to underline her point, columns of black smoke wafted into the sky over west Mosul as Iraqi forces kept up their anti-IS assault with shelling and air strikes.