A series of technical issues have disrupted early voting for the New South Wales election, with the online voting system taken offline and a computer problem disrupting voting at pre-poll booths on Wednesday.

Officials from several political parties told Guardian Australia they had received reports of long delays and even temporary closures of some pre-poll booths on Wednesday morning, including at Woy Woy, Ryde, Balmain and Oatley.

The NSW Electoral Commission confirmed it had detected a “performance issue” with its electronic roll mark-off system.

“This has resulted in intermittent outages of that system at early voting centres,” a spokesman said.

“The issue is currently being examined and is expected to be resolved shortly.

“There are backup arrangements in each early voting centre to allow voters to have their names marked off the roll. Activating those arrangements may result in a delay for some electors in casting their vote.”

The commission said no voting centres were closed. However, Guardian Australia has obtained photos of voting centres in Riverstone and Narooma which have signs on their doors saying “temporarily closed”.

The sign at an early voting centre in Narooma which was temporarily closed. Photograph: Supplied

The commission also confirmed the online voting system iVote was offline.

It said it had received reports on Tuesday of a “usability issue” when people logged in to cast their vote.

“The online voting system will be offline while we address the issue but applications to use iVote are still open.”

Voters going to the electoral commission homepage to register for iVote or postal votes received a message on Wednesday afternoon telling them the site was temporarily unavailable.

This is the message coming up when you go the NSW Electoral Commission website right now and click on the link to register for iVote or postal voting. pic.twitter.com/1pobob4oLJ — Josephine Tovey (@Jo_Tovey) March 13, 2019

Early voting for the 23 March election opened on Monday.

NSW Labor general secretary Kaila Murnain said no one should be turned away from a pre-poll booth.

“We urge the electoral commission to do everything it can to ensure people can vote as and when they arrive at pre-poll booths across NSW.”

NSW Greens MLC David Shoebridge said the issues raised concerns about how the system would manage on election day.

“If the Electoral Commission’s computer system can’t cope with pre-poll, what hope does it have dealing with election day?

“The Coalition has starved most government agencies of funds over the past eight years and now we are seeing the impact with breakdowns like this.”

The electoral commission spokesman apologised for the inconvenience caused to voters.