Japan is bracing for a feared rebound in coronavirus cases as the highways and airports fill with travellers at the start of New Year's holidays, Reuters reports.

The governors of the metropolises of Tokyo and Osaka have urged residents to keep end-of-year gatherings small, as more cases of the Omicron variant of Covid-19 come to light, including a suspected cluster at an Osaka nursing home.

Health officials have advised travellers to avail themselves of free coronavirus tests before departure, amid fears that an outpouring of city dwellers could spread infections to the countryside.

"The highest risk is meeting people without taking adequate measures to prevent infection," said Norio Ohmagari, director of the Disease Control and Prevention Centre and a top health adviser to the Tokyo Metropolitan Government.