Morocco's deadliest earthquake in decades has killed over 2,000 people, authorities said on Saturday, causing widespread damage and sending terrified residents and tourists scrambling to safety in the middle of the night.

The 6.8-magnitude quake struck a mountainous area 72 kilometres southwest of tourist hotspot Marrakesh at 11:11 pm (2211 GMT) on Friday, the US Geological Survey reported.

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

"I was nearly asleep when I heard the doors and the shutters banging," said Ghannou Najem, a Casablanca resident in her 80s who was visiting Marrakesh when the quake hit.

"I went outside in a panic. I thought I was going to die alone."

It is the strongest-ever quake to hit the North African kingdom, and one expert described it as the region's "biggest in more than 120 years."

"Where destructive earthquakes are rare, buildings are simply not constructed robustly enough... so many collapse, resulting in high casualties," said Bill McGuire, professor emeritus at Britain's University College London.

Updated interior ministry figures on Saturday showed the quake killed at least 2,012 people, the vast majority in Al-Haouz, the epicentre, and Taroudant provinces.

More than 2,000 were injured, including 1,404 who are in a critical condition, the ministry said.

The ministry also recorded deaths in Ouarzazate, Chichaoua, Azilal and Youssoufia provinces, as well as in Marrakesh, Agadir and the Casablanca area. (AFP)