Hundreds of offenders have been left unmonitored for more than 24 hours in South Australia following an electronic failure in monitoring devices blamed on a nationwide Telstra outage.

Key points: Department of Corrections was unable to track 774 offenders for 24 hours

Department of Corrections was unable to track 774 offenders for 24 hours An electronic fault in the monitoring devices was reported on Friday morning

An electronic fault in the monitoring devices was reported on Friday morning A nationwide Telstra outage has been blamed for the communication mishap

The Department for Correctional Services in South Australia on Sunday confirmed a communication fault with its electronic monitoring system had left it unable to track 774 individuals who are monitored by electronic tracking devices.

It said that all offenders had been accounted for except for one individual.

The department said the offenders were out for various reasons, including parolees, those on bail and others on home detention supervision.

Chief executive of the department David Brown said the outage was brought to his attention early on Friday morning and service was fully restored by lunch time on Saturday.

"We've got one offender on intensive-bail supervision who had failed to report to his address after he was released by the court on bail on Thursday night and was due to travel to his address on Friday morning," Mr Brown said.

"Any offender who breaches the conditions of an order placed on them by the court is a concern and that offender was deemed suitable to be released on bail by the court and he will answer to the court as to why he failed to comply with the conditions of his bail."

Mr Brown said the department and South Australian police already had a contingency plan in place prior to the fault.

"It was quickly established that it was a network outage with Telstra that was the root cause of the problem," he said.

He said additional staff were brought in to do both phone and home-visit checks on offenders and at about lunch time on Saturday the department had full system functionality back.

SA Premier Steven Marshall said this is a very serious breach and a full investigation would be undertaken. ( ABC News: Nick Harmsen )

'This is a very serious breach'

Premier Steven Marshall said a thorough investigation would be undertaken into why the outage occurred and how to prevent it happening in the future.

He said he was made aware of the outage on Friday and it was "unacceptable" from Telstra.

"Corrections and SAPOL had already done work to identify that this was a potential scenario and therefore put contingencies in place," Mr Marshall said.

"These contingencies were enacted on Friday; the system has now been fully recovered."

He said the State Government would be communicating with Telstra regarding the fault and the safety of South Australian people was extraordinarily important.

"This is a very serious breach, a very serious outage and there will be a full and thorough investigation," he said.

"Clearly this is an unacceptable situation and clearly this is a situation that we cannot afford to occur in South Australia again."

Fault was 'totally unacceptable'

Correctional Services Minister Corey Wingard said he had spoken to Telstra following the outage and the company was aware of how the State Government felt about the communication fault.

Minister for Correctional Services Corey Wingard said he had spoken to Telstra about the outage. ( ABC News: Tom Fedorowytsch )

He said he was made aware that it was a hardware failure that had caused the outage, with a faulty piece of equipment used by Telstra that was "dead on arrival" during a replacement.

"I've spoken to Telstra, this is totally unacceptable, they know very firmly how we feel," Mr Wingard said.

"I have two reports coming from them this week and we'll be doing a thorough investigation as to exactly what went wrong and what we need to do to make sure that this doesn't happen again in the future."

He said he had been reassured by Telstra that the faulty hardware was now back up and running.

Mr Marshall said that following an investigation, further contingencies would be put in place if needed.

"I think one of the things that we will definitely do is benchmark our level of coverage with other states around Australia," Mr Marshall said.

"If we need to take action, if we need to upgrade the system that's exactly and precisely what we will do."

Opposition spokesman Lee Odenwalder said this issue had shown that the current minister in charge of the system was more concerned with other things than really looking after the safety of South Australians.

"One of the most important functions of government is to keep its citizens safe and what we've learnt this morning is that on Friday more than 700 criminals have been left unattended, they've been left unsupervised for 24 hours because of an outage in the Telstra system," he said.

"This comes shortly after an incident in May where the system went down for two hours … it shows that there's a minister that's in charge of the system here who is more interested doing other things … than in really looking after the safety of our people.

"On top of everything we now have a violent criminal on the loose as a result of this outage. This is unprecedented and we need the Government to get on top of this as quickly as possible."

Telstra confirm 'complex issue'

A spokesperson from Telstra confirmed the company had been in ongoing contact with the State Government regarding the network outage.

The company also confirmed the cause of the outage, describing it as a "complex issue" which technicians had worked through on Friday night.

"The issue was caused by a fault in a vendor's network and we had expert technicians onsite to assist them with restoration," the spokesperson said.

"A range of machine-to-machine or M2M services were affected, but the biggest impacts were seen on devices such as ATMs and eftpos terminals.

"The issue was a complex one involving multiple suppliers across a number of locations … we worked through the night to restore services as quickly as possible."