A brush fire forced the evacuation of the historic Mount Wilson Observatory early Tuesday morning.

Hours before sunup, flames could be seen on the hillsides north of Pasadena but motorists on the Foothill (210) Freeway and from just about anywhere with a view of this portion of the San Gabriel Mountains.

“All but two staff members have evacuated. The remaining are on standby to assist firefighting personnel with the observatory’s firefighting systems,” observatory personnel posted on the site’s Facebook page.

The fire threatened several television station operations housed near the observatory. TV stations remained on the air at press time.

The fire broke out about 4 a.m. and burned 30 acres by 10 a.m. So far, the cause of the blaze remains unknown.

The fire is burning in an area where officials conducted “fuel reduction projects” earlier this year “to mitigate impacts of fires like this,” officials with the Forest Service tweeted Tuesday morning.

Crews from the Los Angeles County Fire Department and Angeles National Forest employed water-dropping helicopters equipped with night vision technology to fight the blaze in the early morning hours.

Chantry Flats and surrounding recreation areas were closed.

Approximately 500 firefighters were still battling the brush fire on Tuesday afternoon.