Hersman has said the accident investigation will likely last until the weekend, and on Tuesday reiterated that it is too early to draw conclusions.
“I want to say we’re at the beginning of the investigation. We’re gathering information,” she said.
In the eastern Chinese province of Zhejiang friends and family are mourning the two dead passengers – identified by state media as high-school classmates Ye Mengyuan, 16, and Wang Linjia, 17.
One of the girls may have been run over by an airport fire engine rushing to the scene, San Francisco Fire chief Joanne Hayes-White told reporters on Monday.
According to aviation safety databases, the two dead teens are the Boeing 777’s first fatalities in 18 years of service.