Leave Christchurch on State Highway 73 (SH73) for Arthur's Pass via Springfield. Stop at Springfield to read all about Rewi Alley, the most famous New Zealander ever in China. Carry on SH73 over Porter's Pass to Arthur's Pass village and then over the pass to the West Coast via the Otira Gorge. When you get to Kumara on the West Coast you drive another 7km to the Junction of SH6 and then you have a choice. You either take a 30 minute detour to visit Greymouth by turning right, or you turn left and head to Hokitika. I was born in Greymouth but for my money there's not a lot to see there, it is the biggest town on the Coast (10,000) but you can have a nicer time by staying in Hokitika. It depends where you want to stay the night. It is actually a long way down the Coast to the Haast Pass which is where you cross over the Alps again into Central Otago an Queenstown (all on SH6).
My advice would be to give Greymouth a miss, spend a bit of time looking around Hokitika (as it is the nicest town on the Coast) and then stay the night at Franz Josef, so you can get up early for a glacier glance before travelling on to Queenstown. If you want to break the journey its the logical place, the hotel has a cheap backpackers too and it pays to book ahead. Then be prepared for a long drive of unending forest until you get to Central Otago with a break at Haast for a meal.
Its an amazing journey, I've done it a few times but it is the long way to Queenstown. The road is good and all sealed but quite windy in many places and there are a lot of one-lane bridges (you know the type - give way one way) and you have to watch out for wandering stock (cows) in the Haast Pass.
Gotta go have fun. Highway 73 and 6 all the way to Queenstown. Don't take the Lewis Pass.
Source(s):
Native West Coaster