At 04.00am Lionrock was swirling around the north-western part of the Hoang Sa archipelago, with winds gusting between 60-75kph near its centre.
In the next 24 hours, the storm is set to move north at a speed of approximately 10kph and is likely to gain further strength.
It will then change its course into west north-west and west south-west and approach the Gulf of Tonkin before making landfall on October 11.
Lionrock will likely bring heavy rain, strong winds, and rough seas to parts of central Vietnam starting on October 10.
Weather forecasters warned of heavy rainfall of up to 600mm in the central region that could trigger severe flooding in low-lying areas.
Central localities have made plans to evacuate approximately 300,000 residents from flood-prone areas before Lionrock makes landfall.