Authorities are trying to break up an ice jam that developed on the Delaware River during the frigid temperatures earlier this week, and have extended flood watches and warnings for areas along the river.
The ice jam formed near Trenton. When the ice melts as temperatures rise, flash flooding may occur downstream.
The U.S. Coast Guard says it is sending a cutter to the area in an effort to break up the jam.
The flash flood watch covers Philadelphia, lower Bucks County, northwest Burlington County and Mercer County, and is now in effect through Friday morning, the National Weather Service said today.
And a flood warning is in place through 4 a.m. Friday for parts of Bucks and Mercer counties near the jam. The weather service said the river at Trenton was at 19.9 feet this morning, just below the flood stage of 20 feet.
The jam likely won't break until later today at the earliest, the weather service says. Temperatures around freezing are forecasted for this afternoon, with the mercury expected to reach the low 40s on Friday.
The weather service says the early-season ice jam is unusual, and formed due to the record-cold temperatures over the past week.
At Philadelphia International Airport, a record low was set Tuesday, at 4 degrees. In Trenton, the record low was set Tuesday, at 2 degrees, and tied Saturday, at minus 1.
In some areas, the river ice has begun to crest over the banks, causing damage to fences, sidewalks and docks along the river's edge, the weather service said.
Authorities warn that people shouldn't get too close to ice chunks on river banks.
"The ice jam is an extremely unstable situation as the ice could break without a moment's notice, taking you with it," a weather service forecast discussion says.