Wastewater outlets on the Wellington waterfront are being monitored after a sewage pipe burst outside the library on Victoria Street.
The incident happened at 6am today and the water which initially escaped onto the street was cleaned up.
Crews were trying to work out the extent of the fault and wastewater was being diverted.
Wellington Water said the cast iron pipe was around a hundred years old.
A report published in March found it was "unachievable" for the city to be free from sewage overflows, despite the Wellington City Council setting a target of zero.
The report found Wellington Water was taking, on average, 91 hours for flooding call outs to be fixed and almost three times as long for staff to attend a wastewater issue.
To fix a problem, staff were spending an average of 22 hours - far from its target of six.
Wellington Water chief executive Colin Crampton told the city council its system got overwhelmed as soon as demand spiked.