Canberra's air quality has been rated the worst in the world on Wednesday morning as bushfire smoke shrouded the nation's capital.

The IQAir AirVisual website, which collates air quality information globally, ranked the nation's capital above the likes of Kolkata and Delhi in India.

Twitter - Samantha Maiden

At 10am, the city's Monash air quality station reached an index ranking of 4,091. This is around 20 times above a level considered hazardous.

According to the Canberra Times, the previous highest recorded rating between 2012 to 2019 was 1,420, which was registered on Monday.

The thick smoke is a result of fires that continue to burn on the NSW South Coast.

ACT HEALTH ALERT: Air quality deterioration across the ACT from smoke. Read more at: https://t.co/giX6iUa0eH pic.twitter.com/CzTBjcn2Du — ACT Health (@ACTHealth) December 31, 2019

In a statement, the ACT Government said, "all Canberrans are advised to avoid physical activity outside".

It also advised people who are sensitive to smoke "to remain indoors where possible, with windows and doors closed".

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"The smog, which is impacting the ACT from fires across the border, is extremely thick and expected to linger in the coming days. Conditions may also be intensified by the hot temperatures forecast."

Social media users have been sharing photos and videos of the smoke.

#Canberra’s a ghost town this morning.

Even inside, the smell is sickening.

We’ve been choking on smoke for most of the last month.

And we’re still a month shy of the peak bushfire season.#AustralianFires #canberrasmoke #NewYearsDay pic.twitter.com/71i7ZgZqcL — Hanny Hawkins (@hanny_hawkins) December 31, 2019

This is the main road into Canberra right now. What a way to start a new year.....@abccanberra @abcnews pic.twitter.com/M0iJJ4vkB3 — Michelle Ainsworth (@Ainswort) December 31, 2019

Ramp to Parliament House in Canberra, so close but so much smoke can’t see the flagpole. pic.twitter.com/EQ6J22zgqZ — Linda Mottram (@LindaMottram) December 31, 2019

An apocalyptic start to 2020 in Canberra. I am hiding from the smoke inside next to the air purifier. Looks like the end of the world #Canberrasmoke #AustraliaBurns #ClimateEmergency #auspol pic.twitter.com/04HUr1JtSN — Tara Ellen (@tara_ellen_) December 31, 2019

All the emergency services need more money.... the priorities are all wrong. This photo is Canberra last night. Imagine how bad the south coast is.... pic.twitter.com/Z8EwscZOyj — Liz Volker (@janey1709) December 31, 2019

Parliament House this morning. pic.twitter.com/Pdlfv4sNwr — David Crowe (@CroweDM) December 31, 2019

Smoke has caused problems in Canberra over recent weeks, with a Big Bash match being abandoned there on 22 December as players reported having trouble breathing.

As more than 100 fires continue to burn around NSW, it remains to be seen if the Australia-New Zealand Test will be affected in Sydney this week.

AAP

"There's a bigger picture ... it's heartbreaking what's going on," New Zealand paceman Neil Wagner said on Tuesday.

"It's just a Test match. If it does get affected ... we'll just handle it to the best of our ability."

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On Saturday, temperatures of around 45 degrees Celsius are expected in the west of Sydney with poor air quality forecast.

And smoke from the country's east coast has made its way across the Tasman, with New Zealanders tweeting their concern.

Smoke from Australia in Queenstown, New Zealand. Today vs yesterday. pic.twitter.com/laBw9bHJMQ — 🔆🔥💨📈var = Jason Thompson (@Agent_Jase) December 31, 2019

Additional reporting: AAP