Two teenagers will be charged with lighting a series of bushfires in the NSW Blue Mountains using homemade incendiary devices.

The teens, aged 19 and 13, were arrested at a home they shared in Cascade Street, Katoomba, this morning, after tip-offs from members of the public.

Firefighters at work in the Blue Mountains. Credit:Nick Moir

They are believed to be friends.

They were questioned during the day and acting Superintendent Robert Vella said they would be charged with causing malicious damage by fire.