A suspicious substance has been found in a building carpark in Auckland city.

Police have blocked off traffic going into Customs Street East.

The building is believed to be the Citigroup building at 23 Customs Street East on the corner with Commerce Street.

It is home to many consular offices and diplomatic missions, including the US Consular General.

A police inspector told nzherald.co.nz a 'substance' had been found in the carpark of the building.

Police officers dressed in protective clothing and breathing apparatus entered the building, but re-emerged some time later empty handed.

Major bus routes have been disrupted and an Auckland Bus spokesperson said the company is waiting for advice on how to direct bus traffic.

- NZ Herald staff