Officials have suspended their search efforts after a massive third section of the roof fell at a Latvian supermarket where at least 54 people were killed.

Though no one was injured, officials said they had to consider the dangers of continuing the search in the unstable building.

Latvia's president described the disaster at the Maxima supermarket in Riga, the worst in the Baltic country since it regained independence from the Soviet Union in 1991, as "murder" and called for a speedy investigation into its cause.

We are determined and will do everything in our powers to identify the cause of this tragedy to ensure that nothing like this could ever happen again. - Statement by RE&RE, construction firm

The centre was built by Latvian construction firm RE&RE, which posted a statement on its website saying it was “devastated” by the collapse and extended condolences to the families affected.

“Just like everyone else involved in this tragedy, we are determined and will do everything in our powers to identify the cause of this tragedy to ensure that nothing like this could ever happen again.”

Investigators are looking at faulty construction or work on the roof's grass- and gravel-covered surface as the potential cause of the initial collapse in the crowded supermarket on Thursday. Workers were installing a garden area and children's playground for an adjacent high-rise residential building.

Fire and Rescue Service spokeswoman Viktorija Sembele said the latest collapse occurred in an area where firefighters were not working, but the service immediately recalled its people from inside to ensure there were no casualties. The service tweeted minutes later that no one was injured.

The dramatic cave-in came as rescue workers were attempting to complete an operation in a particularly dangerous part of the building. The rescue service said it wants to consult with engineers before renewing the operation and that all search efforts will be put on hold until Sunday morning.

A view of collapsed Maxima supermarket in Riga shows where a large section of the roof collapsed. (Oksana Dzadan/Associated Press)

Fifty-four deaths had been confirmed by Saturday afternoon. Police spokesman Dairis Anucins said there were still seven people missing who might have been in the store at the time of the collapse.

Associated Press video of the scene showed a large portion of the roof crashing down as rescuers worked close by. A massive boom can be heard as the section hits the ground in a cloud of dust.

President Andris Berzins spoke bluntly about the disaster in an interview with Latvian television, though he did not single anyone out as culpable.

"This is a case where we need to say clearly it is the murder of an enormous number of defenceless people, and that's how we should proceed," Berzins said.

He called for a fast investigation to prevent those responsible from covering up a paper trail and "coming off as pure as angels."

Another 40 injured

Pictures show that a large amount of building materials, including bags of soil for the garden, were left in areas of the roof that Riga city officials say could have been vulnerable to heavy loads.

The store was filled with shoppers when an enormous section of the roof caved in. Slightly over an hour later, while rescue workers searched for survivors, a second and larger section of roof caved in, killing three firefighters.

Laila Rieksta-Riekstina, head of the state's child welfare department, told Latvia Radio that 16 children lost parents in the accident. Three of them lost both parents. Police said there were two Russian citizens and one Armenian among the dead.

Some 40 people were injured, including 13 firefighters who rushed to the scene, and 23 people remained hospitalized as of Saturday afternoon, police said.

The government declared three days of mourning starting Saturday. Latvians streamed to the site in a densely populated neighborhood between downtown Riga and the airport to lay flowers and light candles.

The Fire and Rescue Service has said only 80 square metres of debris remained to be searched as of late Saturday afternoon, but they said it was a difficult section with rubble piled up to 4 metres high.

Police said the investigation could take several weeks to complete. Riga Mayor Nils Usakovs tweeted Saturday that once the investigation is over the supermarket's ruins would be razed and a monument built to the victims. He also suggested that the incomplete residential building might be torn down.