Two gunmen on Tuesday morning stormed Abaqkorey High School in Wajir and opened fired on KCSE candidates sitting the History paper.
However, no one was injured in the morning incident, police said.
The shooting started a few minutes after the examination commenced, forcing students to scamper for safety with their papers.
Habaswein police boss Caleb Wesa said the attackers then fled into nearby bushes as police launched a manhunt for them.
“It was around 11am when they began shooting,” Mr Wesa said.
The students were later regrouped and sat the examination at the nearby Abaqkorey Primary School.
“We could not establish the motive behind the attack but we are investigating the matter,” he said.