Almost 40 minutes after the website crashed, the ABS tweeted: "The ABS & Census websites are currently experiencing an outage. We're working to restore the service. We will keep you updated. Thank you." An error message seen when trying to submit the census. Credit:Liam Phillips Late on Tuesday night, the Bureau conceded the census would remain down at least overnight. The troubles began about 5pm, when people trying to access the form were stopped by messages including a "code 31" error, which said the request "could not be completed because a problem was encountered".

Another error message said the server's DNS address could not be found. Some people were able to get through, but the errors appeared to escalate through the evening until the website stopped responding. One of the error messages received by people trying to complete the census on Tuesday night. Credit:@LornaViking/Twitter

Paul Brebner, a Canberra-based software performance expert who is familiar with the rollouts of large-scale websites, said time and money constraints and the inability to back up the website with a multinational cloud due to privacy concerns may have contributed to the website failing. Mr Brebner said the Bureau of Statistics may have underestimated how many people would try to access their site in peak times, with his analysis predicting as many as 3 million people an hour would try to access the site. The error message received by Glenn when he tried to complete the census on his phone. "If they were expecting 16 million people over 24 hours, that would be okay, but that's not how loads on websites work at all," he said. Richard Macey from Pendle Hill tried to log on to complete his census just after 5pm and repeatedly received an "icon error".

"I'd logged on several times already just to see what it looks like, but tonight I got to the front page of the website, then it says 'icon error'," Mr Macey said. "I gave up in frustration and rang the census number, got through the very first time, and the woman who answered said the system appeared to be overloaded. "She said it could be everyone coming home from work trying to log in at once." Mr Macey ordered a paper form via the hotline and was told if he eventually managed to log in on Tuesday night, he could put the paper form in the recycling. "I just thought they were wanting us all to complete it tonight," Mr Macey said. "I'll wait for the paper one and see what happens."

Glenn, who also attempted to complete the census on Tuesday evening and did not wish to use his last name, was repeatedly served a DNS error from around 5.50pm. He had also logged in successfully in the days prior to the census. "It definitely worked the other day," he said. Others said they had tried to log in on multiple devices and still had no luck getting through, with one person claiming they had tried for two hours before they eventually gave up.

However, some people who managed to fill in their details still faced errors, with messages popping up around 7.30pm that the census could not be submitted as "a problem was encountered". Earlier, the Bureau of Statistics advised anyone who had an error message to wait for around 20 minutes before logging back on. A spokesman said around 7pm on Tuesday that the online system was operating "as expected". "We have currently received more than 1.3 million successful online submissions," the spokesman said. "The system is operating smoothly and as expected. If anyone has experienced a local technical issue, they can try again on another device or contact the Census Inquiry Service on 1300 214 531 if they continue to have technical issues, or go to the Troubleshooting page of the Census website." The Census Inquiry Service was deluged with calls on Tuesday evening, with Census advising anyone with issues to try calling back after August 10.

On Tuesday afternoon, 2016 census manager Duncan Young said census day was going "very well" and online forms would save more than $100 million for taxpayers. "The online form is fast, it's very easy and it's completely secure and Australians are enjoying the experience of filling out their census online," Mr Young said. Loading "The form has the capacity it needs to scale up tonight for the large volumes of response that we are expecting."

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