Natural disaster evacuation plans need an overhaul as the nation heads into its rainy season, experts have warned, saying crowded conditions could spark novel coronavirus clusters that grow into another wave of infections.

The period of heavy precipitation — which typically triggers floods and landslides and often forces hundreds of people to take shelter together in gymnasiums — has already begun in some parts of Japan. A failure to prepare risks reigniting the disease, just as cases decline across most of the country and Prime Minister Shinzo Abe seeks to remove more restrictions and help the ailing economy.

"If a lot of people gather in a small evacuation center and somebody is infected, a cluster will occur and the infection will spread,” said Ichiro Matsuo, an associate professor at the University of Tokyo’s Center for Integrated Disaster Information Research.