A suspicious white powder that forced the Immigration and Customs Enforcement field office in New York City to evacuate was not hazardous, the FBI said. 

Testing of the powder discovered at 26 Federal Plaza, which houses Department of Homeland Security and ICE offices in Lower Manhattan, showed no dangerous substance was involved. 

Sources told CBS News New York there were a total of five envelopes received. The letters contained anti-ICE rhetoric, sources said.

The FBI said the letters were being sent to Quantico for analysis. 

"No injuries or illnesses have been reported amongst the ICE staff or the 40 individuals who were being processed at the facility. Out of an abundance of caution, those being processed for detention were transferred to Delaney Hall and Elizabeth Detention Facility in New Jersey to finish their processing and immigration proceedings. The wellbeing and safety of all detainees remains among ICE's top priorities," DHS Assistant Secretary Tricia McLaughlin said. "This incident comes after months of smears and rhetoric comparing ICE to the Nazi Gestapo and secret police and false claims of 'kidnappings by ICE.' This rhetoric and lies has directly led to our officers facing a 1,000 percent increase in assaults against them. I'm urging sanctuary politicians, activists, and the media to turn down the temperature."

"Let's be clear, this still is a serious crime," New York City Mayor Eric Adams said. 

The FBI is asking anyone with information about the incident to call 1-800-CALL-FBI or to report it online. 

"Anything we can do to assist, we would do so," Adams continued. "It should not have happened and we're going to make sure the person that's responsible will be brought to justice." 

The building was open on Friday. 

Mystery powder found in envelopes at 26 Federal Plaza

Hazmat teams responded to Federal Plaza just before 4 p.m. Thursday after the mystery powder was found inside five envelopes in the mailroom of an ICE field office on the 9th floor. 

Some people in the building were evacuated, while others were ordered to shelter in place after at least two people were exposed to the substance, officials said.

The NYPD urged people to avoid the area before it was determined there was no threat to the public or building workers. No injuries were reported. 

Authorities said the envelopes would be sent to the FBI's headquarters in Quantico, Virginia, for testing.

Building houses federal immigration court

Immigration court is held inside the building and it is where ICE agents have detained people after routine hearings. 

Immigration advocates have clashed with police outside the federal building over arrests and reportedly poor conditions inside the facility. 

A federal judge on Tuesday said he would block the Trump administration from using the building to hold immigrants facing deportation unless it reduces the number of detainees and improves conditions at the site, including by providing sleeping mats and hygiene products.

DHS maintains the building is not a detention center and says allegations of overcrowding or poor conditions are "categorically false."