Smoke from the bushfires in Australian has continued to cause havoc across the state of Victoria, and authorities say any reprieve from Wednesday’s storms will be short-lived.

A third-straight day of thick haze has blanketed Melbourne, with air quality levels deteriorating rapidly this morning.

The haze around the city appears less dense than it was yesterday; however, authorities are still warning people to stay indoors if possible and to avoid any vigorous exercise.

The CBD is currently rated as having “very poor” air quality after earlier being labelled “poor”.

But Melbourne’s eastern and western suburbs, including Box Hill, Footscray, Brooklyn and Mooroolbark, are all considered to be at a “hazardous” level of air pollution.

It comes as some trade workers reportedly coughed up blood on Tuesday as construction companies faced calls for all outdoor work to halt during the smoke haze.

The CFMMEU urged employers Tuesday morning to suspend “dangerous and unhealthy” outdoor work.

It said later in the day that while most sites closed down, work carried on in some locations, including on a Southbank project where a worker was taken away in an ambulance.

Tradies were also said to be coughing up blood on another work site.

Australia Post has equipped its workers with P2 masks, and made wearing them mandatory where air quality was rated very poor or hazardous. But it stopped short of suspending deliveries.

The city’s air quality was rated between hazardous and very poor overnight Wednesday – after taking the title earlier in the week as having the worst air quality in the world.

University of Technology Sydney Associate Professor Brian Oliver found Melbourne CBD’s smoke particle pollution, called PM2.5, was equivalent to lighting up 20 cigarettes when it peaked at 412 Tuesday morning.

It was comparable to 50 cigarettes in Box Hill, where it topped 1000.

Heavy smoke was even forcing firefighters to be rotated away from the front lines.

Royal Melbourne Health respiratory medicine head Lou Irving warned those on the fire ground for more than 60 days could develop chronic bronchitis.

The haze also hampered efforts to fly medical supplies from Sale to isolated and fire-ravaged Mallacoota.

Rain is expected to wash away some of the smoke and bring some relief.

Environmental Protection Authority’s state agency commander Stephen Lansdell said favourable weather conditions would help improve the air quality after wind changes and wet weather reached Melbourne’s western suburbs about 2 p.m. Tuesday.

But he said the smoke was expected to return by Saturday and linger for the weekend.

“On Saturday, we’re expecting a bit of a wind change that’s likely to bring that smoke back from the northeast and East Gippsland, so the north-easterly winds will bring that back,” he said.

He said people should brace for smoke haze to be a problem for multiple weeks.

“I think it’s a good reminder, hopefully these very hazardous conditions over the last couple of days will ease but the fires are going to be lasting for months to come, so we would expect to see impacts in our air quality for a long time yet.”

The weather bureau has forecast a hazy day in Melbourne with a top of 96F.

It said there was a high chance of showers and thunderstorms in the city in the afternoon and evening, with possible heavy rainfall.

Chief Health Officer Brett Sutton said vulnerable groups included children under 14, adults over 65 and anyone with pre-existing medical conditions.