The Trade and Industry Ministry promoted special toilet paper for emergency use as it marked national disaster prevention day.
Officials say that people immediately think of food and water as relief goods but easily forget toilet paper.
But 41 per cent of the country's toilet paper supply comes from Shizuoka in central Japan, one of the country's most earthquake-prone areas.
The government says there will be a toilet paper shortage crisis for about a month if the area is hit by a mega-quake, a lesson learned from the deadly earthquake and tsunami that hit the country in March 2011.
Lack of toilet paper could even cause further discomfort if people start using tissue paper which is not water soluble and could clog up toilets.