An internet outage on the National Broadband Network hit Optus customers across the country on Sunday.

Optus reported NBN outages in Victoria, South Australia, Tasmania, Western Australia and the Northern Territory.

The outage, blamed on a "technical issue," began on Sunday afternoon and continued hours later into the late evening. Optus said services were restored after 11pm.

A stream of Twitter users had reported problems on their NBN home service while at least 1000 complaints were logged by an internet outage site by 7pm.

Some users wanted compensation for the disruption.

In a statement, Optus apologised to customers and thanked them for their patience.

The NBN has been hit with setbacks, cost over-runs, delays and numerous complaints, but the company maintains the rollout will be completed by 2020.

Complaints about the network, however, have risen at a faster rate than the number of new users taking up the fibre-optic internet service, a telecommunications ombudsman report found.

In October, the competition watchdog also urged retailers to change misleading NBN advertising practices, saying advertised speeds should be the minimum download speeds, not the theoretical maximum, since it was confusing customers.