No injuries have been reported but most of the 20 million items the museum contained went up in flames.
Much of the artifacts were feared to have been destroyed.
The National Museum of Brazil in Rio.
"I feel very sorry for my colleagues, some of whom have worked here for 30 or 40 years".
Roberto Robadey, a spokesperson for the fire department, said 80 firefighters were battling the blaze and that by midnight local time it was "just about under control" and should be out within a few hours.
"Collections that are over 100 years old", Cristiana Serejo, one of the museum's vice-directors, told Brazil's G1 news. Vice director Luiz Duarte told O Globo, "We have never had efficient and urgent support".
A firefighter rescues items during a fire at the National Museum of Brazil in Rio de Janeiro
One of the largest anthropology and natural history collections in the Americas was nearly totally destroyed in Sunday's fire in Rio de Janeiro.
"A fire of this scale, the reality unfortunately showed this, we needed a systematic intervention", he said. No humans were harmed as the fire spread across the building, but it could be argued the loss of such records is a dire one for the Scientific community.
"It was a constant worry", he said, adding that he would unplug everything in his office before leaving because of the fire risk.
Employees had recently received training from firefighters in how to prevent and respond to a blaze in the building, Duarte said.
"Luzia is a priceless loss for everyone interested in civilisation", museum director Paulo Knauss told AFP news agency. "History can not be measured by the damage to the building that housed the royal family".
Tropical storm Gordon weakens into depression
Meteorologists are keeping a close eye on the Atlantic now, too, and the season's first major hurricane named Florence. The threat of heavy rains and flooding will continue for several days in the Mississippi Valley, forecasters said.
Riot police fired tear gas outside the park housing the museum on Monday as a small, irate crowd tried to enter.
Marina Silva, a former environment minister and candidate in October's presidential elections said the fire was like "a lobotomy of the Brazilian memory".
"They're burning our history, and they're burning our dreams".
On the massive site where the museum sits, the fencing was dilapidated, stonework was cracked and lawns appeared untended.
The museum had a budget of around $130,000 after incremental budget cuts over several years, which resulted in almost a third of galleries being closed. This year was on track to include an increase from last year.
Dr Barker said it will likely take years for the National Museum to rebuild, although it could be quicker if any items were stored at other locations.
Woodward’s new book depicts Trump’s ‘crazytown’ White House
It ended with Dowd warning that Trump would end up "in an orange jumpsuit" if he went under oath. "He's this dumb southerner ". In Woodward's telling, the president's aides fear not what he might do to them, but what he might do to the country.
"Look at the irony".
In 1879, the Australian Museum exhibited some of its collections in a Sydney International Exhibition building called the Garden Palace. French President Emmanuel Macron offered in a tweet to send experts to help.
The institution's hardships, imposed by budget cuts from the federal government, were well known.
With the cause still under investigation, many already have begun to fix blame, saying years of government neglect left the museum underfunded and unsafe.
NFL Arbitrator Moves Colin Kaepernick's 'Collusion' Grievance To Formal Hearing
Both players have filed a grievance against the NFL, claiming the league has colluded to not sign them due to their protests. The CBA prohibits the league and teams from colluding on decisions about whether a player should be signed.