The two cities, which were devastated in US atomic bombings in the closing days of World War II and have since been rebuilt, said they would set up a committee to study the possibility of a joint bid.
Hiroshima mayor Tadatoshi Akiba, an advocate of nuclear disarmament who has called for the world to be free of atomic weapons by 2020, has previously said he wants the city to host the Olympics in the name of world peace. "We are aiming for the abolition of nuclear weapons in 2020. If we are engaged in Olympic bidding activities in parallel, it is expected to produce a synergetic effect," Akiba told a news conference in Hiroshima.
While the International Olympic Committee's rules state that in principle only one city can host the Olympics, there have been exceptions, such as the 2008 Beijing Summer Games when Hong Kong staged equestrian events.
Hiroshima, which hosted the 1994 Asian Games, and Nagasaki are some 300 kilometres (190 miles) apart. The IOC is due to announce the 2020 host city in 2013. On October 2, Tokyo along with Chicago and Madrid failed in their bids to host the 2016 Summer Olympics, losing out to Rio de Janeiro. Tokyo has yet to decide whether it will bid for the 2020 Games.