Residents described how armed police and men clad in balaclavas stormed the Granby House building on Granby Row, in central Manchester.
The railway was briefly closed during the raid, police said.
A Greater Manchester Police spokeswoman said: "Officers have this afternoon carried out a search at an address in Manchester City Centre as part of the investigation into the horrific incident at Manchester Arena.
"That search is ongoing.
"In order to do this safely we briefly closed a railway line, but it has now been reopened."