Telstra has restored mobile services to thousands of customers who had been unable to send or receive calls.

Calls had been answered with a prerecorded message advising customers the area they are trying to call is “congested”.

A spokesman said a technical issue had affected the network but the issue had been resolved.

Telstra tweeted there had been maintenance on the network overnight and repairs had taken longer than expected.

Mobile, landline and internet services were affected, mainly in New South Wales.

@tokerShark Services are unavailable due to some maintenance we're doing atm - should be working again later on in the morning :-) -Steph — Telstra (@Telstra) June 1, 2015

Many annoyed users took to social media to demand answers from the telco. One Telstra tweet advised a frustrated customer the problem was being looked at and could only say it would be fixed “later this morning”.

The status of Telstra services for specific suburbs can be checked here.