Now is when the popularity of G Shock is blowing through China like a whirlwind.
Right now, G Shock's popularity is blowing through China like a whirlwind.
'Now' is quite common to use with current events. Alternatively, you could use 'right now'. I utilized 'blowing' to bring out more strength in 'whirlwind' to give more power to the claim of popularity of the product. Both sentences retain the same basic meaning.