More than 100 people were taken in for questioning as authorities raided "hijacked" and problem buildings in Hillbrow and the Johannesburg CBD on Wednesday.

Several people rounded up for questioning were surprised by the arrests.

Their building was one of several raided during an integrated "bad buildings" operation carried out by Johannesburg metro police, SAPS, Midvaal traffic police and a security company.

The aim of the raids was to weed out criminal elements and determine if municipal by-laws are being contravened.