“This is a major disaster. It is horrible, it is painful,” the South American nation’s president Irfaan Ali said last night.

The death toll had risen to 20 and several people were injured in the fire at the Mahdia Secondary School in central Guyana, the government statement said.

Ali said he ordered arrangements be made in the capital Georgetown’s two major hospitals “so that every single child who requires attention be given the best possible opportunity to get that attention”.

Private and military planes have been sent to Mahdia, located about 200km south of Georgetown, as the region is affected by heavy rains.

Natasha Singh-Lewis, an opposition MP, called for an investigation into the fire’s cause.

“We need to understand how this most horrific and deadly incident occurred and take all necessary measures to prevent such a tragedy from happening again,” she said.

Guyana, a small English-speaking country of 800,000 people, is a former Dutch and British colony with the world’s largest per capita oil reserves, which it hopes will help spur rapid development.