The mystery "blast" that rocked Kuala Terengganu, Dungun and Marang in Terengganu for several seconds on Friday turned out to be sonic boom from the newly-acquired state-of-the-art Sukhoi fighter jet.

Two of the fighter jets were involved in a non-combatant training in preparation for the Langkawi International Maritime and Aerospace (LIMA) air show.

Royal Malaysian Air Force (RMAF) public relations officer Maj Zulkiflee Abdul Latiff said the fighter jets travelled at supersonic speed, emitting loud sonic booms.

"We hope the people in Terengganu do not panic upon hearing the sound,'' he said.

RMAF cleared the air following reports in the media that the "mysterious blast" shook high-rise buildings, causing some dwellers to run out of their homes.

The Star office in Kuala Terengganu was inundated with calls on Friday from people who wanted to know the cause of the 4.10pm "blast".

Zulkiflee, when contacted, said air force pilots need to undergo training exercises, not only for the air show but also for defence purposes.

Malaysia acquired six Sukhoi fighter jets from Russia recently.

"The fighter jets were flying more than 10,000m above sea level,'' he said, adding that the training exercise commenced on Friday.

"The exercises are being carried out in the interest of the nation,'' he said.