Authorities at the hospital in Piatra-Neamț have told Euronews that their beds are never free of COVID-19 patients.
Romanian police have launched a criminal investigation into a false claim that a COVID-19 hospital is empty.
A misleading Facebook video had suggested that there were no patients at a temporary hospital in the northeastern city of Piatra-Neamț.
Officials at the health centre have told Euronews that the claim is "false" and have called on the authorities to investigate.
Police have said that they are probing the "false news" and are prepared to take "necessary legal measures".
False claims about COVID-19 and vaccinations have been blamed for a recent surge in infections in Romania.
On Tuesday, Romania registered a record 18,863 new infections and 574 deaths -- the first time the country has surpassed 500 deaths in a single day.
The hospital is "filled with COVID-19 patients"
In the Facebook Live video filmed on 14 October, a user films themselves approaching the ATI modular hospital in Piatra-Neamț.
Standing in the courtyard, the user falsely claims that beds at the hospital are empty. The post has been shared more than 3,400 times.
But hospital management has told Euronews that 26 patients were occupying beds on 14 October, all intubated in a serious condition.
"This individual and this group are spreading fake news about the modular from Piatra-Neamț," added Oana Gheorghiu, co-founder of the Daruieste Viata NGO that supports Romanian hospitals.
"[It has been] filled with COVID-19 patients, from the first day it was opened," she said on Facebook.
In a statement to Euronews, Romanian regional police confirmed that they have initiated a criminal case.
The probe was launched "following the appearance in the public space of some images, in which a person presents information about the occupancy rate of the modular hospital in Piatra Neamt," a statement read.
"Police officers ... are carrying out checks with a view to identifying the persons involved and taking the necessary legal measures," said IPJ Neamț spokesperson, Ramona Ciofu.
Those responsible could face charges for "disseminating false news ... knowing their false nature," Ciofu added.
The real-world impact of misinformation
In Romania -- and neighbouring Bulgaria -- slow vaccination rates have been partly blamed on the spread of misinformation.
Unfounded rumours about imaginary side effects have fueled vaccine hesitancy, amid a rapid rise in COVID-19 cases.
Romania's President Klaus Iohannis has pointed to other EU member states and reiterated that COVID-19 vaccines are "safe and effective".
"Vaccination is the only solution to stop the spread of the virus," he said in a Facebook post.
Romania has the second-lowest vaccination rate in the EU behind Bulgaria, with just 34% of adults fully inoculated against COVID-19 compared to the bloc average of 74%.
The ailing Romanian health care system has been stretched to maximum capacity, with more than 1,800 coronavirus patients now in intensive care.
Officials at the temporary hospital in Piatra-Neamț -- which only opened in September -- told Euronews that their beds have never been free.
On Wednesday, the facility held 412 patients with COVID-19, including 24 intubated in a serious condition.
Hospital management added that they are hoping to expand their provisions to provide oxygen to more patients.
The World Health Organization (WHO) has said that it will send a senior expert to Romania to help strengthen the country's pandemic response.
The WHO also plans to provide 34,000 rapid COVID-19 tests and 200 oxygen concentrators to treat virus patients.