Emergency rooms have been unable to treat some patients with serious health conditions due to the extra burden caused by the virus, officials say.
One ambulance carrying a patient with coronavirus symptoms was turned away by 80 hospitals before he could be seen.
Japan, which initially appeared to have the virus under control, passed 10,000 confirmed cases on Saturday.
More than 200 people have now died with Covid-19 and the capital Tokyo remains the worst-affected area.
Groups of doctors at GP surgeries in the city are assisting hospitals with the testing of potential coronavirus patients in order to ease some of the pressure on the health system, officials say.
“This is to prevent the medical system from crumbling,” Konoshin Tamura, the deputy head of an association of GPs, told Reuters news agency.
“Everyone needs to extend a helping hand. Otherwise, hospitals would break down,” he added.