A total of 21 boys were confirmed dead on Saturday after a blaze tore through a school dormitory in central Kenya, a tragedy that has raised questions about safety standards at educational establishments nationwide.

And after night fell, another fire broke out at a girls' school also in the centre of the country, with conflicting reports about injuries.

Earlier on Saturday, the nation's top prosecutor said he had instructed police to look into whether the deadly inferno at the Hillside Endarasha Academy in Nyeri county had been caused by negligence or recklessness.

The flames engulfed a boys' dormitory at the school around midnight on Thursday as more than 150 pupils aged between nine and 13 were sleeping.

Government spokesman Isaac Mwaura said a total of 19 bodies had been recovered from the site and another two had died in hospital.

Of the total 156 boys in the dorm at the time, 139 had now been accounted for, either at home or in hospital, he added.

"It is a catastrophe beyond our imagination," Mwaura said at a press briefing.

The charred bodies of the victims, which police had said were burnt beyond recognition, were found in the dormitory, now a blackened shell with its corrugated iron roof completely collapsed.

Homicide teams and forensic experts stepped up their investigations at the school on Saturday, with DNA tests to be conducted to identify the victims. (AFP)