Waitaki District Health Services chief executive Keith Marshall said the hospital was recently informed GPs would only be available to patients during the day.
"When after-hours care gets withdrawn as it’s being done here, what that will automatically mean is an increase in people coming to ED," Mr Marshall said.
"That will add some pressure, no question."
The hospital has been struggling with a lack of permanent doctors.
It would ideally have 11, but only had five, with the rest made up by locums, Mr Marshall said earlier this month.
Shortages had resulted in the closure of its ED overnight three times in the last two months.
At the time, people were advised to contact the on-call GP unless the situation was urgent.
While the hospital had not been able to recruit any more permanent doctors, it was having more success in finding locum doctors with the help of Te Whatu Ora Health New Zealand (HNZ), he said yesterday.
Minister of Health Dr Ayesha Verrall was set to meet Mr Marshall, Waitaki District Mayor Gary Kircher and deputy mayor Hana Halelele next month to discuss the needs of the hospital.
The health system had been struggling for a long time, Mr Marshall said.
New Zealand needed to do more work on the interface between primary and other types of care, including hospital care.
The notification email he received earlier that month was on behalf of all the GP practices in town, he said.
He attributed the situation to a lack of GPs
, but he understood their position.
"The issue of general practice and primary care for Oamaru — and not just here but nationwide — has been problematic for quite a while.
"You have a whole pile of GP practices who are also really stretched; the doctor shortage isn’t just a hospital one, it’s a nationwide one and it extends to GP practices."
It had now been nearly two weeks since GPs had stopped after-hours services, and the email did not say how long that would last.
Some other areas in the country, such as Ashburton, had not had after-hours GPs for years, he noted.
Area GPs would be switching the phone to Healthline from 5pm until 8.30am, and would only be available on Saturdays and Sundays from 10am-noon and 2pm-4pm.
Healthline could tell callers to go to their nearest ED, but people with unpleasant yet non-serious injuries would understandably need to wait for those in a worse condition to be seen first, he said.
The area has also been struggling with GP practices being unable to take on new patients.
In January, seven GP practices in the Waitaki District were enrolling new patients, but Healthpoint figures accessed this week showed the number had dropped to just two.
WellSouth chief executive Andrew Swanson-Dobbs said the site was a blunt tool, as for example, some practices would still enrol a new patient if they had a family member already enrolled.
GP practices were facing workforce challenges similar to the hospital, he said.
"We need to work together to ensure patients have access to care in the region."
A meeting was planned with Oamaru GP owners, HNZ Southern and the hospital specialist team to collectively find local solutions.