The declaration allows regional governors to urge people to stay indoors, but with no punitive measures or legal force, the measure is far weaker than strict lockdowns seen in other parts of the world.
Abe had already declared a month-long state of emergency in 7 regions, including Tokyo, where a recent spike in cases has prompted warnings that emergency medical facilities could collapse.
"Areas where a state of emergency should be carried out will be expanded from the 7 prefectures to all prefectures," Abe told a special meeting called to discuss the disease.
He said the state of emergency would remain in force until May 6, urging the 126 million people in the country to form a "united front."
With the world's third-largest economy heading for a crippling recession, Abe also unveiled plans to distribute 100,000 yen ($930) to every citizen.
Since the initial emergency came into effect on April 8, several regional governors have called for the measures to be expanded to cover their areas – warning of a growing number of coronavirus infections and overwhelmed medical facilities.
Some have declared their own local emergencies, even though they carry no legal force.
Japan has so far seen a relatively small outbreak of the virus – despite recording its first case in mid-January – with around 8,500 infections and 136 deaths by Thursday.
But local medical associations and experts have sounded the alarm, and Abe has asked people in areas already under a state of emergency to reduce contact with others to avoid an explosive growth in infections.
In Tokyo, the governor has called on people to work from home, and significant drops have been seen in the number of people commuting each day on the city's notoriously crowded transport system.
But while some central areas have been uncharacteristically deserted, local neighborhoods have remained relatively bustling, raising concerns about whether the measures will be sufficient.
Japan's two emergency medical associations this week issued a joint statement warning they are "already sensing the collapse of the emergency medical system," with hospitals unable to deal with patients suffering from non-coronavirus ailments.
And in Japan's third-biggest city Osaka, the mayor has appealed for donations of raincoats to serve as personal protection for health workers who he said were being forced to resort to garbage bags.
Abe said it was critical to avoid travelling within Japan during the Golden Week holiday that begins in late April through to early May.
It is a period where many people travel from the major cities to the country to see family and there are fears this could spread the virus. – Rappler.com