The British maritime traffic controller UKMTO was the first to alert the authorities about the incident on Friday.
"Military authorities have reported that the vessel was boarded by unauthorized personnel while transiting eastward in the Gulf of Aden," writes UKMTO.
Later on Friday, Yemen's coast guard identified Somali pirates as being behind the ship hijacking, AFP reports. The ship is sailing in a southeasterly direction towards Somalia.
According to maritime security firm Ambrey, there are no security forces on board the Tanzanian-flagged ship.
The maritime coalition The Joint Maritime Information Centre (JMIC) raised its alert level to the second highest in early May after several ships off the coast of Yemen were attacked and hijacked by Somali pirates, AFP writes.
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