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A state of emergency has been declared in New South Wales in Australia after the country experienced its hottest temperatures ever.

On Tuesday 17 December temperatures reached 40.9C, but the next day that record was broken again when it reached an average maximum of 41.9C.

When forecasters record temperatures, they take the average of the highest temperatures across a country, because that's the most accurate way to measure a heatwave.

On Tuesday a lot of places reached well above 40.9C. The hottest was in South Australia in a place called Ceduna, where it reached 46.5C.

The previous record was set in January 2013 when it was 40.3C.

Heat like this has meant Australia has had severe droughts and several bushfires.

Authorities in New South Wales (NSW) are currently fighting about 100 fires, in a crisis that has lasted months.

Why is this happening?

Australia has been so warm recently because a band of hot air has swept across it.

The Bureau of Meteorology, which records the weather in Australia, said the main cause is something that's going on in the Indian Ocean.

It's called the Indian Ocean Dipole (IOD) and it's when the western part of the ocean becomes much warmer than the eastern part. This creates a current, which then affects weather conditions.

One chief forecaster called the current "one of the strongest" on record.

What's being done to help Australia?

The prime minister of Australia is called Scott Morrison, he's faced a lot of criticism for not doing enough to help the situation there.

But recently he's pledged to give more money towards firefighters, who are helping to combat the effects of the heat.