A masked man broke into a woman's Fairfax County apartment early Saturday morning and sexually assaulted her before fleeing, police said. 

The 30-year-old woman, who lives in the 7800 block of Lewis Chapel Circle in the Lorton area, awoke about 6 a.m. Saturday to find a man in her bedroom, police said. Police said the man had forced his way inside the apartment.

There were children in the apartment during the assault, police said. They were not harmed. 

The man was described as black, muscular, and about 6 feet tall, police said. He was wearing a black shirt, black pants, and a face mask.

The investigation is ongoing.