Two women have been arrested and charged with arson following a fire at a Hamilton high school.

The 19-year-olds will appear in Hamilton District Court on Wednesday following Friday night's fire which destroyed two science class rooms at Sacred Heart Girls' College.

It took 40 firefighters five hours to put the flames out. Fireworks were found at the scene afterwards. 

Waikato senior specialist fire investigator Peter Hallett, who was at the school on Saturday morning, said it appeared the fire began on the second level of the two-storey block.

Hallett said one classroom, a staff room and resource rooms at the Catholic school were damaged in the fire.

Downstairs classrooms were waterlogged after firefighters spent four hours bringing the fire under control.

Debris was strewn outside the rooms and windows had been shattered.

"Police would like to thank members of the public who provided information which assisted with inquiries," said Detective Sergeant Terri Wilson.

The school says NCEA exams for senior students will continue on Monday as normal while junior students will return to school on Tuesday.

"We are requesting that junior students stay away from school on Monday due to the number on contractors on site and to allow us to complete the post fire clean up," it said in a Facebook post.

"We are confident that the site will be safe for senior students and staff by Monday and that exam conditions will not be compromised."

- NZ Newswire / NZ Herald