Crowds gathered outside Building 35 at Royal Crest Estates as local police and firefighters and a state HazMat truck pulled in Friday afternoon.
Firefighters found several found containers of chemicals, North Andover Fire Chief Andrew Melnikas said, but the chemicals -- acetone and related substances are not hazardous to be around.
Residents of the complex said police were at the building Thursday as well.
There is a criminal investigation into tenants of that building, Police Lt. Charles Gray said, which brought authorities to the building Friday, but he declined to elaborate since the investigation is ongoing.
It's unclear whether or not the chemicals themselves are directly related to an ongoing investigation, but Melnikas emphasized that the chemicals found were not hazardous in and of themselves and residents would be allowed back into the building shortly after.
Police are frequently called to Royal Crest, according to police reports. Crimes most often reported there are car breaks and larceny, but occasionally larger crimes have been reported. In 2009, a resident was charged with operating a massive cocaine ring out of that complex. And in 2011 a man was charged with dealing heroin there.
One resident walked by saying, "All the mold, kids going missing, and now this?"