The police boss said no casualty was reported during the incident.
She said the school had been closed but students who scored Grade D were left behind for tuition. They were at the institution during the incident.
Jerobon said the cause of the fire was yet to be established.
Several residents joined students and teachers in putting out the fire.
Jerobon also led police officers in evacuating those within the school compound as well as ensuring their safety and the institution's property during the incident.
A fire brigade from the Machakos County Government helped in putting out the fire deterring it from spreading to other structures in the school compound.
Mwala MP Vincent Musyoka was among the local leaders who responded to the scene.
Jerobon said the incident was reported to the Masii police station as an arson/fire incident report.
"It was reported by the chief principal of Masii Boys High School Joseph Nzoka that a joint dormitory namely Ndovu and Nyati with a capacity of 230 students caught fire while students were having dinner at the dining hall," Jerobon told the Star.
Jerobon said the scene was visited and processed by her officers led by herself.
"It was established that the dormitory got extensively burnt down and nothing was salvaged. The cause of the fire isn't known and no injuries were reported," she said.
She said the fire was put out by Machakos County Government's fire brigade, students and members of the public.
"The students were later addressed by the area MP, County director of education Margaret Mwirigi among other leaders," Jerobon said.
Jerobon said Directorate of Criminal Investigations detectives attached to Mwala subcounty police headquarters had launched probe into the incident.
