As south-eastern Australia continues to burn amid the bushfire crisis, smoke has crossed the Tasman to shroud New Zealand, and Canberra has recorded unprecedented smoke pollution.

Key points: Canberra's air quality index is 23 times the hazardous rating, rivalling some of the worst in the world

Canberra's air quality index is 23 times the hazardous rating, rivalling some of the worst in the world Heavy smoke from the NSW and Vic bushfires is also blanketing New Zealand

Heavy smoke from the NSW and Vic bushfires is also blanketing New Zealand The ACT Government says it is the worst air quality ever recorded in Canberra

Canberrans woke up to a new year with air quality more than 22 times the hazardous rating.

Smoke from the NSW South Coast bushfires blanketed the capital overnight, with Canberra's south the hardest hit.

The 2:00pm air quality index reading in the ACT's southern station at Monash was 4,650 — more than 23 times the hazardous level of 200.

But the poor conditions did not stop at the border. Many parts of south-eastern Australia are also blanketed in smoke as fires rage on across NSW and Victoria.

Satellite imagery showing the south-east drift of smoke from Australia to New Zealand. ( Supplied: Bureau of Meteorology )

In Batemans Bay, where hundreds of homes and structures are believed to have been lost, the concentration of smoke particles in the air was nearly double that of Canberra.

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Goulburn, to Canberra's north, also suffered poor air quality overnight with the air quality index hitting 2,075 at its worst.

NSW Health has set up special air quality monitoring stations in regional areas to monitor the effects of the bushfires.

But the impact is stretching beyond Australia, with those across the Tasman also noticing heavy smoke.

The huge cloud of smoke generated from the fires has travelled some 2,000 kilometres and blanketed New Zealand's South Island.

Forecaster Tuporo Marsters from New Zealand's MetServices said a strong north-westerly wind was blowing the smoke, which had reduced visibility to 10 kilometres in some areas.

"It's appearing as an orangey haze across Christchurch and places like Timaru," he said.

"It's quite amazing."

Mr Marsters said a cold front moving up the South Island was expected to gradually thin out the smoke-laden air.

Twitter user @getrochelle woke to heavy smoke over Port Chalmers in New Zealand, saying she could smell the smoke from Australia in the rain.

"Since the rain began the smell has become worse. If you have ever been in a burnt/smoke damaged building, that's what it reminds me of out there today," she posted.

Canberra readings off the charts

In the ACT, other air quality stations recorded ratings of 3,436 at Civic and 3,508 at Florey.

The smoke turned the sky orange over Dunedin, New Zealand, with Twitter user @BeneHoltmann capturing this striking image. ( Twitter: @BeneHoltmann )

ACT acting chief health officer Dr Paul Dugdale said the air quality was the worst ever recorded in the capital.

"It is in the highest range that we go up to … and in fact it was out of range overnight on one of our smoke detectors," he said.

"It went off the scale on the small particles.

"It's certainly extremely smoky as anyone can see looking outside."

By 11:30am visibility remained extremely low and people in affected areas were advised to avoid outdoor activity.

"No heavy exercise outdoors — it's not the day to start your New Year's resolution with a morning jog," Dr Dugdale said.

For those going outside, Dr Dugdale recommended wearing a P2 mask, which filters out small PM2.5 particles.

"A P2 mask will help reduce smoke intake into your lungs, but they can be a bit tricky to fit," he said.

"The ordinary surgical masks probably don't do anything particular for your health, but if it feels better and some people are finding comfort from them, then I'm not about to discourage that."