Update at 6:09 p.m.: Fire now up to 10-15 acres. Crews have reportedly "got the upper hand."
A brush fire is burning east of the 241 Freeway near Irvine Lake at the unincorporated Santiago Canyon. So far, the freeway remains open but off-ramps to Santiago Canyon Road have been shut down, according to the CHP.
About 50 firefighters are battling the fire and two helicopters are dropping water.
The exact acreage of the fire is unknown but is "well over five acres," according to ABC-7, and has been burning since 4:13.
Lynnette Round, a spokeswoman for Orange County Fire, says that so far no homes or buildings are threatened.