A TELSTRA spokesman said the mobile service issue impacting Mt Arapiles and Natimuk has been resolved.

"Telstra has replaced the hardware which was faulty restoring mobile services. We've tested services this afternoon and they're back up and running," he said.

Previously:

A TELSTRA hardware fault has caused disruptions to mobile services in Natimuk.

Telstra regional general manager Steve Tinker said the fault was identified on Monday, and was impacting services near Mt Arapiles and Natimuk.

"Our technicians are working to fix the issue as quickly as possible. We apologise to customers who may be experiencing service issues with their mobiles," he said.

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A Telstra spokesman said the fault was unrelated to the mobile network upgrade work occurring in Horsham.

"The issue is not impacting fixed line services which are operating as normal. Customers can continue to use fixed line services including home phones," he said.

"The major upgrade work to Telstra's mobile network in Horsham is proceeding well with works due to be finalised this week. We have worked in smaller work windows and minimised disruption to customers during this time."

Telstra's 3G and 4G mobile services as well as EFTPOS terminals connected to the mobile network could be disrupted during the upgrades.

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