The number of patients attending Kettering General Hospital's Accident and Emergency department has risen by 15 a day compared to the previous year.
It is an "unprecedented" increase, according to hospital staff.
Dr Angela Dancocks, clinical leader of A&E medicine, said: "It certainly has a big impact on the way we can treat our patients."
NHS Northamptonshire is carrying out research to discover why some patients go to A&E instead of their GP.
Kettering General said that between April and July 2010, an extra 15 patients a day were visiting A&E compared to the same period last year. That is an increase of 6.5%.
"Our capacity is limited which means that when we have large numbers of patients coming through the door it's actually very difficult to find free cubicles to put patients in," said Dr Dancocks.
"It's putting an awful lot of pressures on the staff, particularly the nursing staff and junior doctors.
"We're actually seeing staff going off sick because of the stresses that they're put under when it's very busy."
Hospital managers said national research suggests that around 40% of A&E attendees could have been treated elsewhere.
Accident and Emergency departments are meant to be used by people with urgent medical conditions but staff say too many people with minor ailments, such as coughs and colds, are going instead of visiting their GP.
Too many patients are attending A&E with minor ailments
Dr Dancocks said that many patients say they are unable to see a dentist or get a GP appointment: "We see a lot of people with toothache and dental-related problems and they tell us they can't access dental services.
"We also see a number of patients who tell us they have telephoned to get an appointment with their GP but they have been unable to do so for a time that suits them."
The Northamptonshire Primary Care Trust is now researching the reasons why people attend A&E rather than other parts of the NHS.
Richard Alsop from NHS Northamptonshire said they are working with GPs to make sure everyone who needs to can get a same-day appointment: "There are sometimes, I am sure, difficulties in accessing an appointment on the day.
"What I think is important is to work with General Practice so that patients that do need an urgent appointment on the day are able to get that."
The MP for Kettering, Philip Hollobone said the figures for people attending A&E were "startling".
"We've got to get to the bottom of why people can't get the dental treatment they need and can't get the GP appointments they need," said Mr Hollobone.
Another reason for the increasing number of patients at Kettering General Hospital is the county's growing and ageing population.
Northamptonshire is one of the fastest growing areas of the UK. In the last five years the population has grown by around 50,000.
We've got to get to the bottom of why people can't get the dental treatment they need.
Philip Hollobone MP
The proportion of older people in the community is expected to increase by 43,600 over the next decade.
At Kettering General, managers say that hospital beds are already being used by elderly people who should be cared for in the community.
Jayne Tunstall, interim chief executive at Kettering General Hospital, said: "We have been seeing a number of patients coming in whereby they would be better cared for out in the community."
That is the responsibility of NHS Northamptonshire and Northamptonshire County Council.
A £3m business case is being prepared which would result in 18 new specialist care centre beds and six consultant geriatricians to work across hospital and community settings. There would also be additional staff in the Intermediate Care Team.
In October 2010, an End of Life Support Service will be launched which will enable people to die with dignity in their own homes, rather than in hospital.
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