The cases were found in two people from the Yukpa group who live in dire poverty in a cluster of makeshift shelters and tents in the northern border city of Cucuta, according to the National Indigenous Organization of Colombia (ONIC), the country's leading indigenous authority.

Health experts said they fear the coronavirus could spread rapidly among tribes who have little immunity to diseases common in the general population.

Their immune systems often are weakened as well by malnutrition, hepatitis B, diabetes and respiratory diseases like tuberculosis, experts say.

"We are very concerned," Maricela Londono, ONIC press officer, told the Thomson Reuters Foundation.

Several other possible cases are being closely watched in Colombia's indigenous reserves, she said.

About 2 million indigenous people live in Colombia in 115 different groups from the country's northern mountains to the Amazon rainforest in the south.

The 56,000 indigenous families who live near cities and towns are particularly at risk as are those living in border areas, the ONIC said.

The city of Cucuta, where the indigenous cases were found, has been a major entry point into Colombia for Venezuelans fleeing political turmoil in their homeland..

Members of the Yukpa tribe live in both countries.

Colombia has closed its borders with Venezuela, Ecuador, Peru, Panama and Brazil, but people can cross undetected.

"It puts everyone at grave risk," said Londono.

As some tribes only number a few dozen people or less, deaths from the coronavirus mean some communities could face extinction, according to the ONIC and indigenous rights groups.

Earlier in March, indigenous leaders across Colombia told communities to lock down, keep outsiders away, implement social distancing and suspend schools and meetings on ancestral lands.

But only about a fifth of all indigenous communities have enough food to see them through the lockdown, the ONIC said.

Some members of the Yukpa tribe live in Cucuta with little food and no running water.

Last week, in neighboring Brazil a doctor working with the Amazon's largest tribe tested positive for the coronavirus, according to the health ministry.

Brazil's indigenous health service Sesai also reported several suspected cases of coronavirus in indigenous communities.

Colombia has been under lockdown since March 24 and has closed all its national parks, many of which are home to indigenous people.

The coronavirus has infected as least 900 people and killed 16 so far across the South American nation.