ANZ says an outage is preventing some customers from accessing its app or logging into its internet banking website.

The bank tweeted about the outage on Tuesday afternoon, saying it was working to resolve the issue as soon as possible.

The problem persists but ANZ said its ATMs, phone banking, the ANZ Plus app and EFTPOS facilities were still available.

Its rival Commonwealth Bank suffered a similar major outage in March that prevented customers from accessing online services.

AAP