The US-China trade war has descended into “a total war on commodity trade” and new rounds of tariffs will deal a further blow to Hong Kong’s already fragile economy, the city’s commerce chief warned on Tuesday.Secretary for Commerce and Economic Development Edward Yau Tang-wah’s warning was backed up by several business chambers, citing trickling orders from October following a 30 per cent decline in US orders at some mainland China-based Hong Kong manufacturers over the past year.Yau said the…