(MTN NEWS-HELENA) Emergency crews responded to a fire at Helena High School just after 10 p.m. on Monday.

As of midnight, there are still numerous firefighters and police officers at the scene.

Firefighters are working to clear the area room by room, and will remain at the scene throughout the night.

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Damage is said to be extensive, but there is no description at this time of the extent or dollar amount.

The cause of the fire is not yet known.

There have been no reports of injuries.

There is no word yet on how this might affect the school schedule on Tuesday.

We will update you when we get more information.

UPDATE: Classes at HHS have been canceled for Tuesday and Wednesday.

Three teens have been arrested in connection with the fire; their names have not been released yet.

Reporter: Jonathon Ambarian