A fire has gutted the National Museum of Brazil in Rio de Janeiro, the oldest scientific institution in the country. Photo: Facebook

Most of the 20 million items it contained, including the oldest human remains discovered in the Americas, are believed to have been destroyed.

Firefighters are working to put out the blaze. No injuries have been reported.

The museum, which once served as the residence for the Portuguese royal family, celebrated its 200th anniversary this year.

The fire started on Sunday (September 2, 2018) evening, after the facility had closed for the day.

The cause is not known.

Aerial images broadcast on Brazilian television showed it spreading throughout the building.

Brazil's President Michel Temer said in a tweet that it was a "sad day for all Brazilians" as "200 years of work, research and knowledge were lost".

Roberto Robadey, a spokesman for the Rio fire department, is quoted by AP news agency the hydrants closest to the museum were not working and that firefighters had to get water from a nearby lake.

He added that some of the museum's pieces had been rescued.