Time is running out to stop sewage spilling into Wellington harbour

Wellington Water's dealing with a burst pipe - that dates back to the 1900s, and was due for replacement in the next few years.

The nearby wastewater storage system is nearly full to the brim, and it's only a matter of hours before it overflows.

Crews are attempting to cut into the main from a different area and insert a stopper.

Chief Executive Colin Crampton says they need to reduce pressure on the wastewater network, so it's a good idea for CBD workers to stay home.

He says if they can't get the stopper put in ... and resume pumping today, it will be very hard to prevent an overflow.