Initial reports said eight villages in the Biddu district of Ethiopia, close to the border, were covered by volcanic dust.
Villagers have been left without food and traditional springs and streams have been polluted.
The Afar regional government says the numbers affected could rise sharply.
An initial report by the regional government says the situation in border villages is a serious concern.
“Many community members and especially children are reported sick and in desperate need of medical attention,” said Teshome Assefa, of Save the Children.
“Vomiting and retching are common.”
The whereabouts of one community living close to the eruption is unknown.