Sydney and Adelaide are experiencing their hottest April day on record with the mercury soaring above 35 degrees in both capitals.

At Observatory Hill in Sydney at 3pm, the temperature climbed to an unusual 35.4 degrees for this time of year.

The previous record for Sydney was 34.2 degrees on April 6, 2016.

A stunning view from Castlecrag today. (Picture: Chris Walster) (Supplied)

A haze over Sydney was photographed from the air today. (Picture: Emily Wheeler) (Supplied)

West Terrace in Adelaide soared to a sweltering 36.1 degrees at 2.26pm, breaking its previous record of 35.8 degrees in 1938.

It comes as the everlasting summer just keeps on giving with many parts of the country hitting unseasonably high temperatures today.

Temperatures in Sydney, Melbourne and Adelaide have hit about 10 degrees above the April average.

Last week, Sydney recorded its warmest first week of April since 1977 at Observation Hill.

Sydneysiders enjoy the warm weather at Balmoral Beach at midday. (Picture: Cade Thompson) (Supplied)

Sydney Airport hit 36.8 degrees at 2.04pm.

The unusually warm weather is due to a high-pressure system that is bringing a mass of hot air to the country’s south-eastern states.

The blissful conditions are going to stick around for the rest of the week, Weatherzone has confirmed.

Yet, Sydneysiders will feel a cooler change tomorrow with a top of 25 degrees expected but then the rest of the week will see temperatures nudging 30 degrees.

On the weekend, Sydney’s west will be slightly warmer at 32 degrees.

This intense sunrise on the Gold Coast this morning is proving summer has well-and-truly lingered into autumn. (9NEWS) (9news)

As Adelaide has reached more than 35 degrees today, it is the warmest three-day period from Saturday to Monday in April on record.

Tomorrow, the capital will hit a top of 33 degrees, followed by 30 degrees on Wednesday.

However, Thursday will cool off with temperatures dropping to 22 degrees due to a cold front coming over from the western part of the country.

“Parts of South Australia, including Adelaide, are actually in the midst of a late season low-intensity heatwave,” Weatherzone meteorologist Craig McIntosh said.

TODAY weather presenter Natalia Cooper captures the gorgeous weather at Henley Beach today. (Picture: Natalia Cooper) (Supplied)

Hudson Walsh, 14 months, shares an ice cream with his dog Sammy in Adelaide. (AAP) (AAP)

On the contrary, Mr McIntosh said Tasmania was feeling the direct effects of brisk winds and showers with a cold front crossing the state.

However, it looks to weaken and be forced south after clipping southern Western Australia today.

Perth is mostly cloudy and will not see temperatures climb more than 22 degrees until the weekend.

“So heat will remain for many parts of southern Australia, in particular SA, NSW and the ACT well into this coming week,” Mr McIntosh said.

Beachgoers cool down in the water beside Henley Jetty in Adelaide. (AAP) (AAP)

Tomorrow and Wednesday will see temperatures climbing to the late-20s in Melbourne, which will be about 11 to 15 degree above average before a cooler change arrives for Victoria.

For the Commonwealth Games in Queensland, the weather is remaining dry and mostly sunny with tops in the late-20s until tomorrow, which is slightly warmer than the average.

The temperature will slightly drop to the mid-20s on Wednesday before rising again for the weekend.

The seven-day forecast for Darwin looks mostly wet with a chance of a thunderstorm on Wednesday and Thursday.