Tradesmen have been warned to stop work and ask for longer breaks if temperatures plummet to 1C.

Outdoor workers 'should be stood by on full pay' if it gets that cold, according to health and safety guidelines by the Victorian Trades Hall Council.

They are also encouraged to take longer breaks of up to 30 minutes per hour when temperatures drop below 9C.

The guidelines may apply to thousands of workers in the coming days as Australia is battered by a bitterly cold blast of weather from the Antarctic.

Melbourne shivered through its coldest May day in 19 years on Wednesday with the CBC only reaching 10.6C.

Canberra is set to be even colder, with the mercury hitting -4C on Friday morning.

Meanwhile, Sydney, Hobart and Adelaide will have lows between 8C and 4C over the next five days.

Tradespeople 'should be stood by on full pay' when temperatures reach 1C, according to the OHS Reps guidelines (stock image)

According to the OHS guidelines, tradespeople should get half-hour breaks every hour between 4C and 1C, 20-minute breaks between 7C and 4C and ten minutes between 9C and 7C.

Bosses must 'eliminate exposure to extreme cold' by providing heating, shelter and waterproof clothing for their employees, according to Safe Work Australia.

Workers need to be given time to acclimatise to the cold with job rotations, the national guidelines state.

It comes after Melbourne was plagued with icy slush, sleet and black ice on Wednesday.

In regional Victoria, Ballarat also had its coldest May day in 19 years, reaching just 5.7C and recording a light dusting of snow.

'It was just a few sort of flurries... nothing that stuck to the ground,' the weather bureau's Tom Delamotte said.

Working in cold: Health and safety recommendations for employers Outside work in cold weather to be sheltered, screened and warmed with hot air blowers if possible. If the environment cannot be effectively controlled, implementation of an appropriate work/rest regime: for example, paid rest breaks of ten minutes per hour for temperatures between 9C and 7C, 20 minutes per hour for temperatures between 7 and 4C, and thirty minutes per hour for temperatures between 4C and 1C. (An air temperature of 1°C should be regarded as the minimum acceptable for normal work. When the temperature reaches this point, workers should be stood by on full pay.) Workers needing to do work in intentionally cold environments below 1°C - freezers for example - must be provided with appropriate protective clothing and the time they work in such environments must be kept to a minimum. Heated rest rooms or shelters should be provided so those workers may obtain temporary relief from the cold. Provision of hot drinks. Protection of the extremities through the use of appropriate protective clothing, including gloves, insulated or vapour barrier boots, and face masks as necessary. Provision of hot air jets, radiant heaters and appropriate types of gloves and mittens to keep the hands warm and maintain manual dexterity. Insulation or substitution of metal handles and control bars to reduce conductive heat loss. Source: Occupational Health and Safety Advertisement

Tradespeople should get half-hour breaks every hour between 4C and 1C, twenty minute breaks between 7C and 4C and ten minutes between 9C and 7C (stock image)

Workers need to be given time to acclimatise to the cold with job rotations, the national guidelines state (stock image)

At suburban Oakleigh South a driver was killed about 4.40pm when a ute slammed into a tree, with footage from the scene showing ice on the road.

In Victoria's alps, a father and son were rescued after being snowed-in at their hut for two days.

The pair were led through snow-packed trails from Millers Hut, near Mount Wellington, on Wednesday after becoming trapped on Monday.

The warmest place in the state on Wednesday was Mallacoota in the East Gippsland region near the NSW border, which reached 14.9C.

Omeo, also in East Gippsland, hit 7.6C and Hamilton in the state's southwest fell to 8C, while coastal areas recorded large swells.

Temperatures across much of the state fell to 5C below average, and down to 7C below average in some areas.

Showers were recorded along the state's central coast and in parts of Gippsland, including Yarram in southeast Gippsland which received 24.2mm.

Showers are expected to move through Melbourne overnight and into Thursday, with up to 8mm expected.

Thursday isn't expected to bring much relief from the cold, with Melbourne forecast to reach 13C.

A frost warning has been issued for the Northern Country, North East and East Gippsland districts.

'We will see temperatures return to pretty much right on average by Friday across Victoria,' Mr Delamotte said.

Sydney will follow suit with minimums of 8C and 9C on Thursday and Friday, respectively.

Hobart will fluctuate between lows of 4C and 8C over the next five days and maximums as low as 10C.

The South Australian capital will hit a chilly 6C on Friday but remains consistent with maximum temperatures between 14C and 17C in Adelaide.

Many residents took to social media to share videos and images of the icy conditions blanketing much Melbourne and the surrounding southerns region of Victoria