A massive cloud band has caused an unprecedented event, with record rain and cool days across much of Australia's Northern Territories.

The rain is due to a broad upper trough over the area, which is drawing in tropical moisture and dumping it over the tropics.

The Victoria River district had the heaviest rain, with widespread falls of 30-40mm recorded to 9am Wednesday.

Places such as Victoria River Downs had 56mm, their wettest June day in 121 years. Waterloo received 32mm, their wettest June day in 91 years.

Oenpelli had a 71.4mm downpour on Monday - their wettest June day in 94 years, smashing through the last record of 41mm.

This system has also keeping temperatures low for the last few days. Monthly average temperatures in the Alice Springs district are up to 5 degrees below average, lining this up to be the coldest June on record for many towns.