An undersea cable between Perth and Singapore has been cut, affecting Yahoo and Telecom New Zealand Xtra customers.
Customers are experiencing delays of up to two hours sending emails from Xtra email addresses.
Emails are reportedly still being received by Xtra email addresses.
The affected cable is the SEA-ME-WE 3 cable, which is managed by a consortium, including Singtel.
It is reported that the cable was cut around five days ago but Telecom NZ only became aware of the problem from Yahoo, which uses the undersea cable from Perth to Singapore.
Yahoo has re-routed email traffic from the cable while repairs are carried out.
"Telecom will continue to provide updates on its websites regarding expected service restoration but at this stage it is unlikely to be today," the company said in a statement.
Telecom said it does not expect service to be restored by today.
Comment is being sought from Singtel.