POLICE are investigating if arson is to blame for a bushfire that is burning in the Blue Mountains west of Sydney for a second day.

The blaze, which started about 2pm (AEDT) yesterday, has scorched 19ha at Katoomba, west of Sydney, and forced the evacuation of a high school.



Detectives from the Blue Mountains local area command and Strike Force Tronto and the Rural Fire Service will investigate the circumstances of the fire burning between Cliff Drive and Katoomba St.



"Early investigations suggest the fire may have been deliberately lit and investigators will examine the scene closely today," NSW Police said this morning.



Rural Fire Service commissioner Shane Fitzsimmons said westerly winds would make the task difficult for firefighters today as they worked in inaccessible terrain.



"A good fire is still very active, particularly down on the valley floor, so there's a lot of work ahead today for firefighters," he told Channel 7 today.



"You're talking very inaccessible country."



The Blue Mountains missed out on light rain that fell on Sydney shortly before 5am (AEDT) today.



More than 100 firefighters and a water bombing helicopter battled the blaze in Katoomba yesterday.



About half a dozen homes were evacuated as well as some 450 students from Katoomba High School who were moved to a local cinema.



Police also evacuated 25 people from 12 homes because of the thick smoke.



Seven homes sustained minor damage and a garden shed was destroyed.



Crews continued backburning overnight.



Remote area fightfighters will be working today.

Originally published asBlue Mountains bushfire may be arson