Paramedics outside the Queen Alexandra Hospital said they are "spending hours sat waiting to off-load patients".
They said it is having a "massive effect on staff morale" and the "public are not getting the ambulances that they require and that they deserve".
Portsmouth Hospitals NHS Trust said there was an "extremely high demand" at A&E on Monday night.
There were 16 ambulances in the queue at 16:00 GMT, one third of the 46 on duty in Hampshire at the time.
One paramedic for South Central Ambulance Service (SCAS) described the situation as "chaos".
He said: "We're seeing it pretty much on a daily basis and it's having a massive effect on staff morale."
Another, who did not want to be identified, said: "I love my job but every time I log on I know there's potential that I could be put back in that same situation where I'm stuck with a patient at their own home and I can't do anything for them and it's too much, it's too much stress."
A Portsmouth Hospitals NHS Trust spokeswoman said there had been "15 per cent more attendances in the Emergency Department compared to this time last year".
She added: "Last year we received 2,154 more ambulances than any other hospital in the area."
The trust said it had been working with health system partners in an emergency care improvement programme.
Mark Ainsworth, director of operations for SCAS, said he is "increasingly concerned" about ambulances being held at the hospital.
He said patients were waiting for more than two hours outside the hospital.
One third of ambulances on duty in Hampshire waited for up to two hours outside a hospital on Monday.