Forensic investigators and researchers are awaiting access to the fire-ravaged National Museum of Rio de Janeiro to find out what remains of the 20 million artefacts.

After a fire tore through the museum on Sunday, engineers were doing tests on the structure to make sure it would not collapse.

Authorities had expressed concern on Monday that internal walls and parts of the roof were weak.

The museum held Latin America’s largest collection of historical and scientific artefacts, and officials suggested that the damage could be catastrophic, with one official telling a Brazilian news outlet that as much as 90% may have been destroyed.

Brazil Rio Museum Fire
A meteorite on display at the museum after the overnight fire (Leo Correa/AP)

The cause of the fire was not known. Federal police will investigate since the museum was part of the Federal University of Rio de Janeiro.

But protesters, commentators and museum directors themselves said years of government neglect had left the museum so underfunded that its staff had turn to crowdfunding sites to open exhibitions.

Firefighters initially struggled to contain it because the hydrants closest to the museum did not work. Instead, trucks had to gather water from a nearby lake.

Roberto Leher, rector of the Federal University of Rio de Janeiro, said it was well known that the building was vulnerable to fire and in need of extensive repairs.

The institution had recently secured approval for nearly five million dollars (£3.8 million) for a planned renovation, including an upgrade of the fire-prevention system, but the money had not yet been disbursed.

Brazil Rio Museum Fire
The National Museum, seen from above, stands gutted after the fire (Mario Lobao/AP)

On Monday, officials promised 2.4 million dollar (£1.8 million) to shore up the building and promised to rebuild the museum.

“Those saying that the museum will be rebuilt are not telling the truth,” said Luiz Philippe de Orleans e Braganca, an heir to Brazil’s last emperor.

“The building could be rebuilt, but the collection will never again be rebuilt. Two hundred years, workers, researchers, professors that dedicated in body and soul (to the museum) … the work of their life burned due to the negligence of the Brazilian state.”

The museum, whose main building was once home to the royal family, had extensive paleontological, anthropological and biological specimens.

It also contained a skull called Luzia that was among the oldest fossils ever found in the Americas.

It held an Egyptian mummy and the largest meteorite ever discovered in Brazil — one of the few objects that officials could confirm had survived. Some parts of the collection were held at others sites and thus spared.

Luiz Fernando Dias Duarte, the museum’s deputy director, said that anything held in the main building was likely destroyed, and Cristiana Serejo, a vice-director of the museum, told the G1 news portal that maybe around 10% of the collection had survived.