Tokyo: At least 27 people were reported killed Wednesday while 10 were missing in torrential rain lashing Hiroshima prefecture in western Japan, authorities said.

The Japan Meteorological Agency (JMA) sounded an alert in the mountainous region where an unprecedented amount of rain fell in only 24 hours, triggering floods and landslides.

Police and firefighters received around 20 calls about people buried or swept away by the flooding of canals and rivers, according to Kyodo news agency.

Among the fatalities was a two-year-old boy buried under mud in a rural area and a man who was washed away near Hiroshima, where the Nenotanigawa river burst its banks.

A firefighter participating in rescue operations also died, state television channel NHK reported.

Authorities have advised the evacuation of around 65,000 people living in 26,000 houses in the mountainous region most affected by the rain.

Prime Minister Shinzo Abe said he had sent "hundreds of troops" of the Japanese Self Defence Forces (SDF) to help with rescue operations, according to NHK.

More than 200 policemen have also been despatched to Osaka city and nearby provinces.

Abe interrupted his summer vacation in Yamanashi to coordinate the operations and has given instructions to make "all possible efforts" to help those affected, he said in remarks to media.

The Japanese TV channel showed images of houses destroyed in the landslides, cars buried under debris or overturned, flooded streets and destroyed farms.

The high number of casualties and material damage was due to the intense rainfall combined with the soft terrain of the region, along with the location of many homes on foothills, Japanese media reported.