The blast shook the island as heavy rains triggered flooding which killed three people, the president told reporters on Thursday, calling for a minute of silence.
Footage broadcast on national television showed streets covered in deep mud and strewn with debris and uprooted trees.
A statement released by President Wavel Ramkalawan's office said "following an explosion at the CCCL explosives store that has caused massive damage to the Providence Industrial area and the surrounding areas and major destruction caused by flooding due to heavy rains, the president has declared a State of Emergency for today the 7th December."
"Everyone is being asked to stay at home. All schools will be closed. Only workers in the essential services and persons traveling will be allowed free movement," the statement added.
The government's official Visit Seychelles account on X said the international airport and ferries between its islands remained operational for tourists.
The Seychelles, a major tourist destination, is made up of 115 islands and is the least populous country in Africa with about 100,000 people.
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