At least 22 people were killed and 16 others injured overnight when two adjacent buildings collapsed in Fez, one of Morocco's oldest cities, the prosecutor said on Wednesday.

One building was unoccupied, while the second was hosting an Aqiqah, a traditional Muslim celebration marking the birth of a child, the Fez prosecutor stated in a press release.

The prosecutor said the death toll was preliminary and that an investigation has been opened.

Eight families lived in the building where the celebration was taking place, they said.

A survivor, who lost his wife and three children, told local Medi1 TV early that rescuers had been able to retrieve one body, but he was still waiting for the others.

State-owned broadcaster SNRT News footage showed rescue workers and residents digging through the rubble.

"My son, who lives upstairs, told me the building is coming down. When we went out, we saw the building collapsing," an old woman wrapped in a blanket told SNRT News, without giving her name.

SNRT News reported that witnesses at the scene stated the buildings in the Al-Mustaqbal neighbourhood, a densely populated area in the west of the city, had exhibited signs of cracking for some time.

Besides the judicial probe, a technical and administrative investigation has also been launched to determine what caused the four-storey buildings to collapse, local authorities said in a statement.

The buildings were erected in 2006 as part of a government scheme under which residents of shantytowns in the city build their own homes on allocated plots.

Fez, a former capital dating back to the eighth century and the country's third-most-populous city, was among cities caught up in a wave of anti-government protests two months ago over deteriorating living conditions and poor public services.

Adib Ben Ibrahim, housing secretary of state, said in January that approximately 38,800 buildings across the country had been classified as being at risk of collapse.

Wednesday's collapse is one of the worst in Morocco since the fall of a minaret in the historic northern city of Meknes, which killed 41 people in 2010.

Most of Morocco's population, financial and industrial hubs and vital infrastructure are concentrated in the northwest, with the rest of the country reliant on farming, fisheries and tourism.

In October, youth-led unrest revealed deep-seated anger over poverty and public services as the government pushes on with ambitious infrastructure projects and the opening of modern stadiums ahead of the 2030 FIFA World Cup.

Fez, one of the cities to host the World Cup and this month's African Cup of Nations soccer tournament, has some of the country's poorest neighbourhoods.