More than 45,000 customers of internet provider iiNet have been without services in Western Australia since at least Sunday evening.

Around 45,753 iiNet customers across WA have been unable to connect to the internet after what the company's website described as a "major fault".

iiNet said the issue was "identified" shortly after 9pm on Sunday, after broadband customers complained about being disconnected and being unable to reconnect to the internet.

While updates have been provided through the company's website, no estimated time of restoration has been given.

Many customers took to Twitter with complaints.

"No internet again today @iinet?!" Twitter user Rashas Moustaches said.

Others suggested they had been offline since well before Sunday evening.

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"Internet still down. Been well over 24 hours now. Something has too be done soon?" Mark Lanney wrote.

"This is so frustrating! I've had no internet for over 24 hours now," fellow user Beck said.

Updates posted on the iiNet website said the impact was "on-going for some NBN and DSL Fetch TV customers in Western Australia".

"Engineers are continuing to work with our vendor to identify the root cause of the issue," the website said.

"Works are also currently underway to redirect affected customers to alternate networking hardware to reduce impact."

Glenn Parnell runs Hyper IT in Perth, a company that provides IT support and advice for businesses across the state.

Mr Parnell said he started getting calls from clients around 11am on Sunday, who were expressing connection problems.

Mr Parnell said a cinema chain had been affected experiencing problems with its online booking system, while restaurants and bars were having problems with eftpos machines and online ordering systems.

"The biggest one is probably eftpos," he said.

"If you can't actually take sales from your patrons and you put up a big cash only sign, that of course has its own issues."

iiNet has been contacted for comment.

The latest update from the provider stated: "Engineers are performing works. NBN services continue to be affected along with some broadband customers."

The Perth-based telecommunications provider purchased rival company Westnet for $81 million in 2008.