Updated 8.50am

A powerful earthquake that struck Morocco Friday night has killed at least 632 people and injured 329 others, the country's interior ministry said on Saturday.

Of those injured, 51 were in a critical condition, the ministry said, after the 6.8-magnitude quake that struck 72 kilometres (45 miles) southwest of tourist hotspot Marrakesh.

Strong tremors were also felt in the coastal cities of Rabat, Casablanca and Essaouira.

Previously, the ministry had said that at least 296 people died in the quake, which sent terrified residents fleeing their homes in the middle of the night.

"We felt a very violent tremor, and I realised it was an earthquake," Abdelhak El Amrani, a 33-year-old in Marrakesh, told AFP by telephone.

"I could see buildings moving. We don't necessarily have the reflexes for this type of situation. Then I went outside and there were a lot of people there. People were all in shock and panic. The children were crying and the parents were distraught."

"The power went out for 10 minutes, and so did the (telephone) network, but then it came back on," he added. "Everyone decided to stay outside."

The quake "killed 296 people in the provinces and municipalities of Al-Haouz, Marrakesh, Ouarzazate, Azilal, Chichaoua and Taroudant", Morocco's interior ministry said in an initial statement before the interior ministry announced the higher death toll.

'Unbearable' screams

Faisal Baddour, an engineer, said he felt the earthquake three times in his building.

"People went out into the street just after this total panic, and there are families who are still sleeping outside because we were so scared of the force of this earthquake," he said. "It was as if a train was passing close to our houses."

Frenchman Michael Bizet, 43, who owns three traditional riad houses in Marrakesh's old town, told AFP that he had been in bed at the time of the quake.

"I thought my bed was going to fly away. I went out into the street half-naked and immediately went to see my riads. It was total chaos, a real catastrophe, madness," he said.

The 43-year-old shared video of piles of rubble from collapsed walls in the streets.

Footage on social media also showed part of a minaret collapsed on Jemaa el-Fna square in the historic city.

An AFP correspondent saw hundreds of people flocking to the square to spend the night for fear of aftershocks, some with blankets while others slept on the ground.

Houda Outassaf, a local resident, told AFP he was walking around the square when the ground began to shake.

"It was a truly staggering sensation. We're safe and sound, but I'm still in shock," he said.

"I have at least 10 members of my family who died... I can hardly believe it, as I was with them no more than two days ago."

Fayssal Badour, another Marrakesh resident, told AFP he was driving when the earthquake hit.

"I stopped and realised what a disaster it was... The screaming and crying was unbearable," he said.

The interior ministry said authorities have "mobilised all the necessary resources to intervene and help the affected areas". 

The regional blood transfusion centre in Marrakesh has called on residents to donate blood for those injured.

In the town of Al-Haouz, near the epicentre of the quake, a family was trapped in the rubble after their house collapsed, local media reported.

Significant damage likely

"We heard screams at the time of the tremor," a resident of Essaouira, 200 kilometres west of Marrakesh, told AFP.

"People are in the squares, in the cafes, preferring to sleep outside. Pieces of facades have fallen."

The USGS PAGER system, which provides preliminary assessments on the impact of earthquakes, issued a red alert for economic losses, saying extensive damage is probable and the disaster is likely widespread.

Past events with this alert level have required a national or international level response, according to the US government agency.

Internet connectivity was disrupted in Marrakesh due to power cuts, according to global internet monitor NetBlocks.

Moroccan media reported it was the most powerful earthquake to hit the country to date.

German Chancellor Olaf Scholz offered condolences, while Indian Prime Minister Narendra Modi said he was "pained" by news of the quake.

The earthquake was also felt in neighbouring Algeria, where the Algerian Civil Defence said it had not caused any damage or casualties.

In 2004, at least 628 people were killed and 926 injured when a quake hit Al Hoceima in northeastern Morocco, and in 1960 a magnitude 6.7 quake in Agadir killed more than 12,000.

The 7.3-magnitude El Asnam earthquake in neighbouring Algeria in 1980 was regionally one of the most destructive earthquakes in recent history.

It killed 2,500 people and left at least 300,000 homeless.