Meanwhile, heavy rain watches are in place for the Westland ranges and Fiordland north of Doubtful Sound, and a strong wind watch has been issued for inland Canterbury.
These come as a front, preceded by a strong and moist north-west flow, is forecast to move onto southern New Zealand tonight.
The front will move northwards over the remainder of the South Island tomorrow.
Burrows said Westland would experience a period of heavy rain until 8am tomorrow.
Showers are picking up in the region, with the main period of heavy rain still to come.
Aucklanders awoke to a thick blanket of fog this morning, causing flight delays and cancellations. Photo / Kerri Graham
Burrows advised people to try to avoid low-lying areas, drive cautiously, and to ensure their gutters and drains were clear of debris.
She said there is potential for slips, surface flooding and rising water levels in streams and rivers.
The main area of concern is in the ranges in the Westland district.
While there is a moderate chance the weather watch will be upgraded to a warning, Burrows said the weather had not reached warning criteria levels at this stage.
Fiordland’s heavy rain watch came into play at 11am and will stay in place until 10pm, with a low chance of being upgraded to a warning.
Rainfall as high as 7mm had accumulated within the first few hours of the warning, with more heavy rain yet to hit the region.
In Canterbury, strong north westerly winds have been forecast until 6am on Monday, with Mt Cook airport recording 75km gusts earlier today.
A strong wind watch is in place for the high country and the plains near the foothills, and has a moderate chance of being upgraded to a warning.
The winds are set to gradually increase and sustain until the end of the watch period, easing before dawn.
Janhavi Gosavi is a Wellington-based journalist for the New Zealand Herald who covers news in the capital.