President Wavel Ramkalawan has asked people to stay indoors as a precaution after the blast. / Photo: AP

Seychelles has declared a state of emergency after a blast at an explosives depot and heavy rains damaged an industrial zone and surrounding areas.

"Everyone is being asked to stay at home. All schools will be closed. Only workers in the essential services and persons travelling will be allowed free movement," President Wavel Ramkalawan said in a statement on Thursday.

The explosion had caused "massive damage" to the Providence Industrial zone and surrounding areas on the main island of Mahe, the statement said , while flooding due to rains had resulted in "major destruction".

The statement gave no details on the cause of the explosion or if there were casualties.

Seychelles is made up of 115 islands and is the least populous country in Africa with about 100,000 people.

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