Four elderly patients at a hospital in Gifu Prefecture have died after the air conditioning unit in their rooms broke down amid a heat wave that continues to grip the country, police and the medical institution said Tuesday.

Y&M Fujikake Daiichi Hospital, however, denied that the air conditioning failure was the cause of death, saying that fans were put into use after the air conditioning units malfunctioned.

The police received a report on Monday evening that four people had died at the hospital possibly due to heatstroke after the air conditioners broke down. They have since launched an investigation, suspecting it could possibly be a case of professional negligence resulting in deaths.