Swarms of desert locusts that have been devouring crops and pasture in the East Africa region have spread to South Sudan, the United Nation's Food and Agriculture Organization has said.
The FAO said about 2,000 adult insects had entered South Sudan via Uganda into the southern county of Magwi.
The UN has warned that a food crisis could be looming in East Africa if the outbreak is not brought under control. The invasion is the worst infestation in Kenya for 70 years and the worst in Somalia and Ethiopia for 25 years. Swarms have also spread into Tanzania, Eritrea, Djibouti and Uganda.
Desert locusts can travel up to 150 kilometres in a day and eat their own body weight in greenery, meaning a swarm of just one square kilometre can consume as much food as 35,000 people in a day, according to the UN.
Efforts to control the locust infestation have so far not been effective.
Aerial spraying of pesticides is effective in diminishing the swarms but countries in the region do not have the right resources.
Sudanese Agriculture Minister Onyoti Adigo Nyikuac said the government was training people to spray.
"Also we need chemicals for spraying and also sprayers. You will also need cars to move while spraying and then later if it becomes worse, we will need aircraft," he said, according to AFP.
Several million South Sudanese are already facing hunger as the new country struggles to emerge from a civil war.
About 60 per cent of South Sudan's population is facing food insecurity — and destruction of harvests by locusts could lead to a drop in nutrition levels in children, rights group Save the Children has warned.
Even without the locusts, the charity expects that more than 1.3 million children aged under five will suffer from acute malnutrition this year. Up to 25 million people are suffering after three consecutive years of droughts and floods.
The FAO fears that the locusts — already in the hundreds of billions — and eat their own body weight in food every day, are breeding so fast that numbers could grow 500 times by June.
The FAO last week called on the international community to provide nearly US$76 million to fund the spraying of the affected areas with insecticide.
The US Secretary of State Mike Pompeo has pledged $8 million to help fight the invasion on his visit to Africa.
Mr Pompeo was speaking after talks with Abiy Ahmed, the prime minister of Ethiopia, which has called for "immediate action" to deal with the problem affecting four of the country's nine states.
Somalia has declared a national emergency in response to the crisis. Uganda has deployed soldiers to the northern regions to spray pesticides. And Kenya has deployed aircraft to spray pesticides in several region.