Two buildings collapsed in Fez’s Al-Mustaqbal area; one hosted an Aqiqah ceremony with eight families living inside.
Survivors and witnesses said the structures had visible cracks; judicial and technical probes are underway.
The disaster comes amid national concerns over unsafe buildings, with 38,800 structures flagged at risk earlier this year.
In Fez, one of Morocco's oldest cities, two nearby buildings collapsed overnight, leaving at least 22 people dead and 16 injured, the prosecutor said on Wednesday.
According to a statement from the Fez prosecutor, one building was empty while the other was holding an Aqiqah, a customary Muslim celebration commemorating the birth of a child.
An inquiry has been launched and the death toll is preliminary.
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 witnesses at the scene as saying the buildings in the Al-Mustaqbal neighborhood, a densely populated area in the west of the city, had shown signs of cracking for some time.
According to a statement from local authorities, in addition to the judicial investigation, a technical and administrative investigation has been launched to find out what led to the collapse of the four-story structures.
The structures were constructed in 2006 as part of a government initiative that allows city shantytown dwellers to construct their own houses on allotted plots.
Two months ago, Fez, the third most populated city in the nation and a former capital going back to the eighth century, was one of the cities engulfed in a wave of anti-government protests about worsening living conditions and subpar public services.
In January, housing secretary of state Adib Ben Ibrahim reported that some 38,800 buildings nationwide were deemed to be at danger of collapsing.
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.
