NEWARK, N.J. (TNND) — Four detainees from a privately run immigration detention facility in Newark remained unaccounted for on Friday after an uprising broke out over poor conditions, according to authorities.

Lawyers told The New York Times that Delaney Hall went into lockdown on Thursday after law enforcement officials responded to reports of a "disturbance" inside the center.

Migrants reportedly revolted over the quality and timeliness of meals, family and lawyers said in interviews.

Mayor Ras Baraka issued a statement early Friday morning, "demanding immediate answers and clear communication with the GEO group and the Department of Homeland Security."

"We are concerned about reports of what has transpired at Delaney Hall this evening, ranging from withholding food and poor treatment, to uprising and escaped detainees," the statement read. "This entire situation lacks sufficient oversight of every basic detail - including local zoning laws and fundamental constitutional rights. This is why city officials and our congressional delegation need to be allowed entry to observe and monitor, and why private prisons pose a very real problem to our state and constitution."

After word got out that inmates were upset about delayed meals, protesters could be seen outside the facility pushing against gates and attempting to block vehicles.

A senior DHS official told The Associated Press more "law enforcement partners" were brought in to help find the detainees. The identities of the escaped have not been released.

American Friends Service Committee said in a statement that people inside the center reported getting small portions of food, with breakfast at 6 a.m., dinner at 10 p.m. and no lunch.

The 1,000-bed immigration jail in New Jersey was opened this year by Immigration and Customs Enforcement (ICE) under a 15-year, $1 billion contract as part of President Donald Trump's mission to crack down on illegal immigration.

Newark was one of four New Jersey cities sued this year over so-called sanctuary policies.

There is no official definition for sanctuary policies or sanctuary cities. The terms generally describe limited local cooperation with Immigration and Customs Enforcement. ICE enforces U.S. immigration laws nationwide but sometimes seeks state and local help.

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Editor's note: The Associated Press contributed to this article.