The US Coast Guard responded after 8am to reports of the fire and dispatched a helicopter and two boats, Petty Officer First Class Matthew West said.
Local fire departments, including those from Philadelphia and Wilmington, Delaware, also responded.
A tugboat was moving the unmanned barge at the time of the fire, West said, adding there were no injuries.
The Delaware Bay is an estuary of the Delaware River.
Ship traffic also was not affected by the fire that was still burning several hours later, he said.
The barge appeared to be standing still as boats on both sides of it fired water cannons into the piles of burning metal.
Smoke billowed from several fires aboard the boat, and its location was shifting to the New Jersey side of the bay.
West said the cause of the fire remained under investigation.
In a statement, the Delaware Department of Natural Resources and Environmental Control said the barge was being moved to shallower water and that it was on the scene performing air monitoring.
26°C