The bug was caused by computer systems accidentally adjusting the devices' clocks to daylight saving time.

Queensland opted out of the annual switchover to DST in 1972, putting it an hour behind New South Wales for part of the year.

Subscribers to Virgin Mobile and Optus' networks were affected.

The ABC news network reported that some customers set off for work without realising there had been a mix-up, causing earlier-than-normal traffic on the roads.

"I was thinking it does seem a little bit darker," it quoted one Brisbane office worker as saying, who had arrived at work to find it closed.

Caffeine was involved in both networks' attempts to placate angry customers.

Optus posted a message on Facebook, offering a free cup of coffee to subscribers who showed their smartphones to barristas at a city centre Brisbane cafe.

Virgin, by contrast, offered to deliver a meal to vulnerable people living in Australia if users uploaded pictures of their own earlier-than-normal morning lattes.

(BBC News)