The ease in restrictions comes in response to Puerto Rico governor's request to waive the Jones Act, which limits shipping between US ports to US owned-and-operated vessels, to ensure there was no impediment to bringing in supplies.
US President Donald Trump temporarily lifted restrictions on foreign shipping from the US mainland to Puerto Rico on Thursday to help get supplies quickly to the US territory as it reels from the devastation of Hurricane Maria.
But even so, the island still faces huge logistical hurdles to distribute badly needed food, fuel and drinking water.
Most of the Caribbean island's 3.4 million people also are without electricity.
Shipping containers have been piling up at Puerto Rico's ports in the aftermath of Maria, which struck on September 20, causing widespread flooding and major damage to homes, roads and other infrastructure.
TRT World's Giles Gibson reports from Washington DC.
Puerto Rico's governor, Ricardo Rossello, had sought a waiver of the Jones Act, which limits shipping between US ports to US owned-and-operated vessels, to ensure there was no impediment to bringing in supplies.
The waiver, which will be in force for 10 days and will cover all products shipped to Puerto Rico, was signed on Thursday morning by acting Department of Homeland Security Secretary Elaine Duke, the DHS said in a statement.
Duke told reporters on Thursday she was "very satisfied" with the federal response to Maria. "The relief effort is under control. It is proceeding very well," she said.
The US government has periodically lifted the Jones Act for a temporary period following violent storms, including after hurricanes Harvey and Irma, which hit Texas and Florida in late August and earlier this month.
Critics had charged the government was slow to issue such a waiver for Puerto Rico after Maria, which was the most powerful hurricane to hit the island in nearly 90 years.
Trump had issued a temporary waiver for the shipping of petroleum on September 8, soon after the departments of Defense and Energy made recommendations to do so in response to Harvey, which hit Texas on August 25 damaging refineries and pipelines.
No federal departments recommended a waiver for Puerto Rico, however, leaving the requests to lawmakers and Puerto Rico’s governor.
Even as FEMA and the US military have stepped up relief efforts, many residents have been exasperated at the prolonged lack of electricity, reliable supplies of drinking water and other essentials.
In the old town in the capital, San Juan, a smattering of shops were beginning to open but there was still a lack of basic services.
Radamez Montañez, a building administrator from the municipality of Carolina, east of San Juan, said he had been without water and electricity at home since Hurricane Irma grazed past the island earlier this month. "It's chaos, total chaos," he said. "Everybody is in total chaos."
Critics of the Trump administration have said the island is not getting the same response from Washington as it would if it were a US state, even though its residents are US citizens.