Up to 50 Palmerston North Boys' High School pupils and teachers were sent home on Friday after an outbreak of a stomach bug at the school's boarding facility.

The school's deputy rector, Gerard Atkin said all students were well today, but two teachers remained sick.

He said he was unsure of the exact number of students hit by the outbreak, guessing "about 19 or something."

However, rector David Bovey estimated 20 teachers and between 20 and 30 pupils were sick.

"A small number of boys missed exams," Atkin said.

Those students would apply for a derived grade based on their marks during the year, he said.

A spokesman for the Palmerston North District Health Board said the school called about the outbreak on Friday and the health board "supported them".

He said at that stage they had already sent all the students home from the College House hostel.