More than 1,000 people have been killed and a further 1,200 injured in an earthquake near Marrakesh that flattened homes and devastated mountain villages in Morocco.

The Interior Ministry said on Saturday the death toll had reached 1,037, with 1,204 injured, 721 of them critically.

The casualty toll was expected to climb as rescuers reached remote areas and dug through rubble for survivors or bodies.

State television showed people clustered in the streets of Marrakesh, afraid to go back inside buildings that might still be unstable. Many wrapped themselves in blankets as they tried to sleep outside.

The magnitude 6.8 quake late on Friday was the hardest to hit Morocco in 120 years and it toppled buildings and walls in ancient cities made from stone and masonry not designed to withstand quakes.

Bill McGuire, professor emeritus of geophysical and climate hazards at University College London, said: “The problem is that where destructive earthquakes are rare, buildings are simply not constructed robustly enough to cope with strong ground shaking, so many collapse resulting in high casualties.

“I would expect the final death toll to climb into the thousands once more is known. As with any big quake, aftershocks are likely, which will lead to further casualties and hinder search and rescue.”

In a sign of the huge scale of the disaster, Morocco’s King Mohammed VI ordered the armed forces to mobilise air and land assets, specialised search-and-rescue teams and a surgical field hospital, according to a statement from the military.

Despite an outpouring of offers of help from around the world, the Moroccan government had not formally asked for assistance, a step required before outside rescue crews could deploy.

In Marrakesh, the famous Koutoubia Mosque, built in the 12th century, was damaged, but the extent was not immediately clear.

People also posted videos showing damage to parts of the famous red walls that surround the old city, a Unesco World Heritage site.

Rescuers worked through the night, searching for survivors in darkness, dust and rubble.

Most of the tiny village of Moulay Brahim, carved into a mountainside south of Marrakesh, was uninhabitable after walls crumbled, windows shattered and more than a dozen homes were reduced to piles of concrete and bent metal poles. At least five residents were trapped.

The head of a town near the earthquake’s epicentre told Moroccan news site 2M that several homes in nearby towns had partly or totally collapsed, and electricity and roads were cut off in some places.

Abderrahim Ait Daoud, head of the town of Talat N’Yaaqoub, said authorities are working to clear roads in Al Haouz province to allow passage for ambulances and aid to populations affected, but said large distances between mountain villages mean it will take time to learn the extent of the damage.

The Moroccan military deployed aircraft, helicopters and drones and emergency services mobilised aid efforts to the areas hit by damages, but roads leading to the mountain region around the epicentre were jammed with vehicles and blocked with collapsed rocks, slowing rescue efforts.

World leaders offered to send in aid or rescue crews as condolences poured in from countries around Europe, the Middle East and the G20 summit in India.

Turkey’s president, whose country lost tens of thousands of people in a massive earthquake earlier this year, was among those proposing assistance.

France and Germany, with large populations of people with Moroccan origins, also offered to help, and the leaders of both Ukraine and Russia expressed support for Moroccans.

The US Geological Survey said the quake had a preliminary magnitude of 6.8 when it hit at 11.11pm local time. The agency reported a magnitude 4.9 aftershock hit 19 minutes later.

The epicentre of Friday’s tremor was near the town of Ighil in Al Haouz province, roughly 43 miles south of Marrakesh.

Friday’s quake was felt as far away as Portugal and Algeria, according to the Portuguese Institute for Sea and Atmosphere and Algeria’s Civil Defence agency, which oversees emergency response.