Hospital managers have since removed the sign. A spokeswoman said she was unable to say whether its placement was unauthorised.
Genter said she was in the area and visited and A&E after being told that the sign had been put up.
She was also told there was such a push for space at the hospital that chairs and sofas had been moved out of rooms to make more space for patients.
"They are obviously under a high degree of pressure. The staff are doing their best in really difficult circumstances.
"To me, this is evidence of failure by the National government. They're delivering for New Zealanders who are most well off."
She said Minister of Health Dr Jonathan Coleman was "completely out of touch", having a North Shore electorate where people could afford either health insurance or private health care.
When the NZ Herald pointed out to Genter that Coleman was a medical doctor, she replied: "He hasn't been a doctor for a while now, has he?"
Counties Manukau District Health Board acting chief executive Dr Gloria Johnson said the sign had been removed.
"The hospital is frequently 'over full'. We advise staff each day when this is happening to ensure timely discharges and efficient bed management."
She said that the hospital - at midnight - was inside the six-hour target the government has set for waiting times at A&E.
Johnson said: "This is despite a very busy Friday evening when more than 400 patients were seen. Credit is due to our very hard-working staff for achieving this."
She said this year had seen "unprecedented acute demand" as had other health boards in Auckland.
"Some patients may sometimes experience a longer than six-hour wait, especially if they need referral to other specialist services. However, last night we met our six-hour target."
The six hours is measured from the time someone arrives until they leave - a stark difference from the rogue sign which told patients they faced a wait of eight hours before they were seen.
Ministry of Health figures show the South Auckland health board missed the government's A&E target in the most recently reported statistics - April to June - with 92 per cent of people seen in six hours or less.
Applied to Friday night's patient numbers, that would mean at least 32 people would have waited longer than six hours.
Over the two years prior to those statistics, the health board was either on the government target at 95 per cent or slightly above at 96 per cent.
Coleman came into Parliament in 2005 as MP for Northcote and became a Cabinet minister in 2008. He qualified as a doctor at Auckland University, and worked as a house surgeon in Hawke's Bay and Auckland before training as a GP in the UK. He worked as a GP in London.
His Beehive biography stated he returned to New Zealand in 2001 and "worked in clinical medicine and in management consultancy for PricewaterhouseCoopers".
Coleman, who did not respond to a request for an interview, sent a statement through a spokeswoman which paid tribute to "all the health professionals at Counties Manukau for their continued hard work".
"Pressures do arise in any busy ED, especially in during the winter months," he said, saying it wasn't too late to get a flu jab.
He said research showed the 95 per cent six-hour health targets for A&E would save about 700 lives. While his statement noted Middlemore Hospital's current 92 per cent rate, it didn't explain the impact of missing the target.
Coleman said the DHB's funding had gone up $470 million since National was elected, with $57m this year for a total of $1.5 billion.
