Auckland, Sept 8 NZPA - Telephone services have not been badly affected by today's big aftershock in Christchurch but users are still being urged to stay off their cellphones if they can.

Telecom said the 5.1 magnitude aftershock shortly before 8am briefly interrupted services in central parts of Christchurch but most service were soon restored.

The 111 emergency service was fully available. Telecom said its land line and cellular networks were all performing well.

Telecom said its mobile networks dealt with a very high number of calls after this morning's big aftershock and it urged people to minimise the use of mobile phones for anything other than important calls and to limit the sending of images and video on mobile broadband.

Telecom is not charging for local, national and mobile calls using its payphones around Christchurch but said calls should be brief restricted to important issues.

Chorus, the company which looks after the physical telephone network, said 100 people had been sent to Christchurch to help restore telephone services.

Vodafone said its cellular network was working well and was not under undue stress because of the big aftershock today.

Vodafone spokesman Paul Brislen said some cellular sites were on generators but most were back on mains power.

"It is business as usual for our network," Mr Brislen said.

"Customers have been particularly good about keeping things short. Congestion hasn't been a problem at all."