(Reuters) - A powerful earthquake in Morocco has killed more than 800 people and injured hundreds more, the country's deadliest tremor in more than six decades, toppling houses in remote mountain villages where rescuers dug through rubble for survivors.

A local official said most deaths were in mountain areas that were hard to reach.

Residents of Marrakech, the nearest big city to the epicentre, said some buildings had collapsed in the old city, a UNESCO World Heritage site, and local television showed pictures of a fallen mosque minaret with rubble lying on smashed cars.

Pan-Arab al-Arabiya news channel reported that five people were killed from one family, citing unnamed local sources.

The Interior Ministry, in its televised statement on the death toll, urged calm and said the quake had hit the provinces of Al Haouz, Ouarzazate, Marrakech, Azilal, Chichaoua and Taroudant.

Montasir Itri, a resident of the mountain village of Asni near the epicentre, said most houses there were damaged. "Our neighbours are under the rubble and people are working hard to rescue them using available means in the village," he said.

Further west, near Taroudant, teacher Hamid Afkar said he had fled his home and there had been aftershocks following the initial quake.

"The earth shook for about 20 seconds. Doors opened and shut by themselves as I rushed downstairs from the second floor," he said.

Morocco's geophysical centre said the quake struck in the Ighil area of the High Atlas with a magnitude of 7.2. The U.S. Geological Survey put the quake's magnitude at 6.8 and said it was at a relatively shallow depth of 18.5 km (11.5 miles).

Ighil, a mountainous area with small farming villages, is about 70 km (40 miles) southwest of Marrakech. The quake struck just after 11 p.m. (2200 GMT).

The earthquake is Morocco's deadliest since a 2004 tremor near Al Hoceima in the northern Rif mountains which killed over 600 people.