(CNN) A heat wave in southern Japan has killed at least eight people, dealing another blow to a country still recovering from the worst flooding in decades.
Six people died on Saturday, and two people on Sunday, Kyodo News reported, as thousands sought medical treatment for heat stroke and heat exhaustion.
Of 33 people who sought medical help in Hiroshima Sunday, three were volunteers who were helping with the clean up, according to the city's disaster management office.
The heat wave struck the same prefectures where flooding and landslides killed at least 210 people last week, compounding the already difficult recovery ahead.
Nineteen people remain missing or unaccounted for from the floods, and 64,000 personnel are still conducting search and rescue operations, officials said Monday.
Temperatures reached a scorching high of 38.8 degrees Celsius (101 degrees Fahrenheit) in Ibigawa, Gifu prefecture on Sunday. Several locations, including Kurashiki City in Okayama and Asakita Ward in Hiroshima, recorded the highest temperatures so far this year, according to Japan's Meteorological Agency.
As the floodwater rose last week, thousands sought shelter in evacuation centers, which are said to be equipped with air-conditioning. Images from one center in Kurashiki City, Okayama, show evacuees sitting in front of fans.
Tens of thousands of households remain without electricity and water. That, combined with the heat, is making the clean up operation far worse.
The World Meteorological Organization defines a heat wave as a period where temperatures are at least five degrees Celsius greater than the average high temperature for more than five consecutive days. In Japan, current temperatures are between four to seven degrees Celsius higher than normal in many cities, according to CNN Meteorologist Michael Guy.
The flooding was especially devastating to Japan's aging population. About 70% of the flood victims were aged 60 or above.
These elderly victims were more vulnerable due to their ailing health, restricted movement, and lack of access to information -- the same factors that now place them at risk for heat strokes and other heat-related dangers.
The flood had already brought on a slew of health concerns. Floodwater can contain contaminants such as toxic waste and chemicals, as well as infectious diseases that survive better in water than on dry land. Now, the flooded buildings and mud combined with the heat and humidity create a new health hazard -- widespread mold and mildew.
This isn't Japan's first fatally hot summer: a heat wave in August 2013 set the record temperature of 41 degrees Celsius (105.8 degrees Fahrenheit) and killed dozens.
Officials are warning cleanup workers and volunteers to take breaks and stay hydrated, as the Japan Meteorological Agency has forecast high temperatures for the rest of the week.