Mayor Nutter urged residents in flood prone areas to evacuate as Hurricane Sandy intensified, calling the response thus far "decent."
As of noon, some 300 residents of Philadelphia and the surrounding Pennsylvania suburbs had left their homes for shelters.
An estimated 10,000 city residents live in areas at risk of serious flooding, and officials have urged that they consider staying with family or friends, or move to shelters.
"Part of the challenge here for us is to strike an appropriate balance between non nonchalance and utter horror and fear," the mayor said at a noon press conference at West Philadelphia High School. "If you looked outside this morning, you might think, it's not so bad. All we can stress is it's going to get progressively worse."