THE elderly, our young and pets are at risk as low-intensity heatwave conditions lurk ahead for north-eastern NSW.

BoM said temperatures will ramp up for a few days from Saturday, and NSW Ambulance has issued a warning with temperatures set to reach the mid to high 30s by the end of this week.

A stream of northwesterly winds will transport a pool of hot air from central Australia across NSW during the second half of this week.

According to the Bureau of Meteorology, a low-intensity heatwave will affect many areas of western NSW between Wednesday and Friday.

The hot air will contract to eastern and northeast NSW from the weekend, where a low-intensity to locally severe heatwave will continue into the start of next week.

Temperatures in Casino are expected to sit around 33C until Saturday where mercury will soar to 36C.

Other towns such as Kyogle and Lismore will also experience temperatures around 35C on this day, before temperatures drop a few degrees on Sunday before rising again from Monday to around 32-35C.

Both NSW Ambulance and the Bureau of Meteorology are advising people of all ages to take care and avoid the extreme heat.

"Heat can kill (so) it's important that people are alert to the symptoms associated with heat exhaustion in themselves or others, especially young children and the elderly," NSW Ambulance Chief Superintendent Alan Morrison said.

"These include nausea, faintness, dizziness, loss of appetite, weakness, headache, and vomiting," he said.

Figures show that from 1 December 2017 to 31 March 2018, Paramedics treated 4451 patients for dehydration, were called to 175 drownings or near drownings and responded to 227 people suffering from heat exhaustion.

NSW Ambulance aeromedical teams were called to 1536 jobs including a number where the patient was suffering from severe heat exhaustion and dehydration and required transport via helicopter to hospital.

Bureau of Meteorology NSW/ACT Manager of Weather Services Jake Phillips said the heat is already building in the west of the state and it will continue to intensify over the next day or two while at the same time spreading east.

"One of the characteristics of heatwaves is not just hotter maximum temperatures but also hotter minimums," he said.

Mr Phillips said this is the first heatwave of the season, and coming off the back off relatively mild conditions it will potentially have more impact on the community than normal for a low intensity heatwave.

NSW Ambulance Chief Superintendent Alan Morrison said within an hour, the temperature inside a car parked in the sun on a 35C day can reach highs of 47C or more.

"Never leave children or animals in a car unattended even if you think it's only going to be for a minute. This can lead to fatal consequences even with a window open," Chief Superintendent Morrison said.

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