New Jersey's governor on Friday ordered state police to assume control outside a migrant detention centre in Newark that has become a weeklong flashpoint for clashes between protesters and federal Immigration and Customs Enforcement agents.

Governor Mikie Sherrill, a Democrat, said she was acting to quell escalating tensions and episodes of violence outside Delaney Hall, the 1,000-bed jail operated by the private company Geo Group on behalf of ICE.

Sherrill, who has repeatedly called for the closure of Delaney Hall, said the aim was to ensure both freedom of assembly and public safety.

"I will not give ICE the pretext to expand operations in our state," Sherrill told a press conference, joined by state Attorney General Jennifer Davenport and acting state police Superintendent Jeanne Hengemuhle.

Other US cities have experienced mass deployments of ICE agents, with President Donald Trump claiming that federal immigration officers needed reinforcements to safely do their jobs.

State police moved in on Friday to set up "protected protest zones" beyond the gates to give demonstrators safe places to gather, and have established vehicle checkpoints to control traffic flow, state police Lieutenant Colonel David Sierotowicz told reporters.

"ICE agents and their partners have agreed to remove themselves from the immediate area," he said.

Officials said that anti- and pro-ICE protesters would be kept apart in separate assembly zones.

DHS chief welcomes move

In a message posted to social media on Friday, US Homeland Security Secretary Markwayne Mullin cast the moves by New Jersey officials as a "win for law and order" and thanked the governor for "allowing New Jersey State Police to cooperate with us."

He added that Sherrill acted after days of "refusing to allow state police to assist @ICEgov law enforcement against violent anti-ICE rioters."

Protesters confronted by ICE agents have gathered daily outside Delaney Hall since late last week, after immigrant detainees contacted relatives and supporters to announce a labor and hunger strike demanding their release and calling attention to conditions they described as inhumane.

Among the complaints they listed were "food containing worms in a state of decay," faulty ventilation, unsanitary bathrooms and unchecked spread of influenza-like illness inside the facility.

Mullin has denied the allegations, saying detainees are provided with adequate calories and sanitation, but "it isn't a Holiday Inn."

The facility has held more than 850 immigration detainees, only about a 100 of whom had criminal convictions, according to the Deportation Data Project, which gathers and analyzes US government figures.

Trump weighed in this week at a White House Cabinet meeting, calling Delaney Hall "a nice facility" that is doing a great job.

"These aren't protesters, these people are fake," he said, alleging without evidence that people rallying outside the detention center were being paid to protest.

ICE agents have periodically clashed with protesters, using batons and pepper spray. Six protesters were arrested on Wednesday, according to Mullin. US Senator Andy Kim of New Jersey, who came to support protesters, was pepper-sprayed at the protest early this week.

Sherrill joined protesters on Memorial Day and attempted to visit the facility, but ICE denied her access. Instead, she listened to a detainee account on a phone call from outside. Mullin called her attempt "nothing more than a political stunt."

"The people inside Delaney Hall are fathers and mothers, sons and daughters, and members of our community," Sherrill said in a statement. "In New Jersey, we believe in the rule of law and that everyone deserves to be treated with basic dignity."

On Thursday, several officials of the New Jersey Health Department visited Delaney Hall but were only allowed to inspect food service and the kitchen. As of Friday, their findings have yet to be released.