The telco is working to restore mobile services to a huge portion of southern NSW after not one but two cables 230km apart were damaged, wreaking havoc on dozens of mobile sites on the local network.

Telstra's mobile network was interrupted on Tuesday evening, leaving much of the region and south-western NSW without service.

A back-up line was lost at Barmedman when a power issue was caused by mice damaging the equipment needed for transmission, and then the main line was cut several hours later near Adelong.

The widespread outage has left thousands of square kilometres of the Riverina without a mobile connection and several towns without ADSL.

"It's two separate issues in two separate locations that's caused a big outage," a spokesperson for Telstra said.

"As we can see, it proves the mouse plague affects everyone from farming to technology."

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Power technicians were arranged to attend the Barmedman site on Wednesday afternoon, the spokesperson said.

The nature of the Willigobung location and terrain within the Bago State Forest "means we are unable to identify cause" or timeframe on repair, they said.

The outage didn't affected the major Riverina centres of Wagga and Albury but it has hit across western and southern areas, including Griffith and Coleambally, across to Hay and Moulamein and south along the Murray River border towns, Telstra's southern region general manager Chris Taylor said.

"It's always hard to say how many customers there are that roam on mobile sites, but if you look at the population of those towns [as a start], it's thousands," he said.

More than 1000 ADSL customers in Griffith, Hay, Mathoura, Deniliquin, Whitton and surrounding areas remain without internet as a result of the saga.

A small number of landline phone services in Maragle and Tumut were also cut.

The telco said it is working hard to restore service but could not put a timeframe on getting service reconnected.

"The trouble is when people are on the road or travelling, or out on a property, that's where we need to get them connected," they said.

"We know how important it is for people to stay connected, and are treating these repairs with our highest priority."

Earlier

A widespread Telstra outage has left thousands of square kilometres of the Riverina without a mobile connection and several towns without ADSL.

The telco is working to restore mobile services to a huge portion of southern NSW after not one but two fibre cables 130km apart were cut, wreaking havoc on dozens of mobile sites on the local network.

Telstra's southern region general manager, Chris Taylor, confirmed staff were inspecting the cables on Wednesday morning after the series of unfortunate events.

It began on Tuesday evening when a back-up line was cut near Temora, which was then exacerbated when main one was damaged at Adelong several hours later.

"At about 5.30pm [Tuesday] we had a fibre cut near Temora that didn't affect any services but it was our redundant, or back-up, fibre for most of the infrastructure in the area," Mr Taylor said.

"Then a few hours later we've had another cable cut near Adelong, which has taken the main line ... that's caused an impact on 44 mobile sites."

The damage was caused "by independent construction in the area", Telstra said on its website.

The outage hasn't affected the major Riverina centres of Wagga and Albury but it has hit across western and southern areas, including Griffith and Coleambally, across to Hay and Moulamein and south along the Murray River border towns, Mr Taylor said.

"It's always hard to say how many customers there are that roam on mobile sites, but if you look at the population of those towns [as a start], it's thousands," he said.

Telstra wasn't yet in a position to put a timeframe on the repairs, as fibre-optic teams were still on-site assessing the situation.

The fix could be a quick one and resolved within a couple of hours or a longer process, depending on the damage, Mr Taylor said.

A spokesperson for the company confirmed that fixed services aren't affected - with the exception of some customers impacted around Maragle and Tooma - and that landlines and NBN should still be operating as normal.

More than 1000 ADSL customers in Griffith, Hay, Mathoura, Deniliquin, Whitton and surrounding areas are also unable to establish an internet connection.

"The trouble is when people are on the road or travelling, or out on a property, that's where we need to get them connected," they said.

"We know how important it is for people to stay connected, and are treating these repairs with our highest priority and we apologise for any inconvenience when unforeseen damages like this takes place."

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