Six Brazilian tourists were found dead of carbon monoxide poisoning Wednesday inside an old apartment where they were staying in central Santiago.

Authorities said police were alerted by the Brazilian Embassy, which had been called by one of the victims when she became ill.

When officers entered the apartment in a six-story building they found four adults and two children dead, police commander Rodrigo Soto said. The fire department said a high concentration of carbon monoxide was measured in the apartment, which it said was completely closed.

Firefighters prepare to enter an apartment where six Brazilians died of apparent carbon monoxide poisoning in Santiago, Chile, Wednesday, May 22, 2019. Police commander Rodrigo Soto said officers found four adults and two children dead at the six-story building. The fire department said a high concentration of carbon monoxide was measured in the apartment, which it said was completely closed. (AP PhotoEsteban Felix)

Firefighters prepare to enter an apartment where six Brazilians died of apparent carbon monoxide poisoning in Santiago, Chile, Wednesday, May 22, 2019. Police commander Rodrigo Soto said officers found four adults and two children dead at the six-story building. The fire department said a high concentration of carbon monoxide was measured in the apartment, which it said was completely closed. (AP PhotoEsteban Felix)

An investigation was underway to determine the source of the leaked carbon monoxide, which is a colorless and odorless gas produced by fuel combustion in gas stoves and heating systems. A heavy accumulation can cause death.

Santiago registered its coldest day of the South American autumn early Wednesday, with the temperature dropping to zero Celsius (32 Fahrenheit).

Firefighters work on a snorkel platform over an apartment where six Brazilians died of apparent carbon monoxide poisoning in Santiago, Chile, Wednesday, May 22, 2019. Police commander Rodrigo Soto said officers found four adults and two children dead at the six-story building. The fire department said a high concentration of carbon monoxide was measured in the apartment, which it said was completely closed. (AP PhotoEsteban Felix)

Firefighters work on a snorkel platform over an apartment where six Brazilians died of apparent carbon monoxide poisoning in Santiago, Chile, Wednesday, May 22, 2019. Police commander Rodrigo Soto said officers found four adults and two children dead at the six-story building. The fire department said a high concentration of carbon monoxide was measured in the apartment, which it said was completely closed. (AP PhotoEsteban Felix)

 Chilean police talk with neighbors in front a building where six Brazilians died of apparent carbon monoxide poisoning at an old apartment in Santiago, Chile, Wednesday, May 22, 2019. Police commander Rodrigo Soto said officers found four adults and two children dead at the six-story building Wednesday. The fire department said a high concentration of carbon monoxide was measured in the apartment, which it said was completely closed. (AP PhotoEsteban Felix)

Chilean police talk with neighbors in front a building where six Brazilians died of apparent carbon monoxide poisoning at an old apartment in Santiago, Chile, Wednesday, May 22, 2019. Police commander Rodrigo Soto said officers found four adults and two children dead at the six-story building Wednesday. The fire department said a high concentration of carbon monoxide was measured in the apartment, which it said was completely closed. (AP PhotoEsteban Felix)