The intense heat is expected to affect a number of large population centres with the heat likely to stretch from the western border to areas near the coast. 

The heat will also to build through this week and people are warned they should not expect a reprieve until at least the weekend in many areas.

Daytime temperatures will be close to (or exceed) 40 degrees over large areas of the state from Tuesday through to Friday. 

The western half of the state will see daytime temperatures climb above 45 degrees. Canberra is forecast to reach close to 40 degrees each day through until Friday.

The Hunter and Western Sydney are forecast to reach close to or above 40 degrees through until Saturday. Overnight temperatures will also be unusually warm in many places

It may not drop far below 25 over the western half of NSW, while some locations in the far west will only drop to about 30 degrees at night.

The heatwave conditions are expected to bring elevated fire risks across NSW and the ACT throughout the week. 

A Fire Weather Warning and Total Fire Ban are already in effect for NSW Southern Slopes for Tuesday.

Heatwave conditions can also have a significant impact on people's health and the community is warned to avoid strenuous activities where possible, remain hydrated and check on the safety of older or vulnerable members of the community. 

With school holidays currently underway, it is particularly important to consider the impacts of the heat on children and what holiday activities bring additional risk.