Auckland and Christchurch are about 620 miles (1000 kms) apart. They're at opposite ends of the country—Auckland towards the top of the North Island, and Christchurch about half-way down the South Island—so the quickest way to get from Auckland to Christchurch is to fly. There are other options, too, for travelers who want to make a journey out of it.
Duration: 1.5 hours
Several flights travel from Auckland to Christchurch every day. They leave from the domestic terminal at Auckland Airport. As they only take around an hour and a half to travel more than 600 miles, flying is by far the easiest way of traveling between Auckland and Christchurch.
By Car and Ferry
Duration: 2+ days
Many travelers to New Zealand like the flexibility of renting a car. Driving between Auckland and Christchurch is not the quickest way to get there, but few travelers would make the journey in one go, opting to stop at many points of interest along the way, including the Tongariro National Park, Taupo/Rotorua, Wellington, Picton, and Kaikoura.
To drive between Auckland and Christchurch, you'll first need to get to Wellington. The quickest route heads south on State Highway (SH) 1 through Hamilton and Matamata (of Hobbiton fame), and skirts Lake Taupo and the Tongariro National Park. This route takes about eight hours, directly. The journey can also be taken though the west of the North Island, via New Plymouth and Mount Taranaki, east via Rotorua and Napier, or even further east via Tauranga and Gisborne.
Once you've reached Wellington, you'll need to take the InterIslander Ferry across the Cook Strait to Picton, at the top of the South Island. Ferries leave several times a day from the Wellington InterIslander Ferry Terminal, just north of the central city, from the early hours of the morning through to the late evening. The crossing takes about three hours. It's extremely scenic on a good day, especially as it sails through the Marlborough Sounds. However, it can also be rough when there's been bad weather, and is sometimes canceled if the sea is too rough.
At Picton, continue driving south. The most direct route follows SH 1 through Blenheim and Kaikoura, along the east coast of the upper South Island. Driving directly, the journey from Picton takes about five hours, but the popular whale-watching town of Kaikoura is worth at least a day.
A longer way to reach Christchurch from Picton is to head west to Nelson on SH 6, then along the West Coast between Westport and Greymouth, across Arthur's Pass and the mountains, and east across the Canterbury Plains to Christchurch. This is a much longer journey than taking SH 1 from Picton, but is worthwhile if you stop at many places along the way.
By Bus and Ferry
Duration: 2+ days
The simplest route outlined above (Auckland to Wellington through the Central North Island, and then Picton to Christchurch along the east coast of the upper South Island) can also be traveled by long-distance bus. These leave Auckland in the early morning or in the evening, for an overnight service. You can either book individual legs of the trip so you can spend time in places of interest en route, or travel straight through. If booking straight through from Auckland to Christchurch, tickets usually include the InterIslander Ferry between the islands.
By Train and Ferry
Duration: 2+ days
New Zealand's passenger rail network is not extensive, but the journeys that are possible are extremely scenic. Advantages of taking the train are that it's more environmentally friendly than driving or flying, and you can enjoy the views without having to watch the road. Plus, the trains are more spacious than buses, and are equipped with bathrooms and a dining cart.
To get all the way from Auckland to Christchurch by train you'll need to take two different services: the Northern Explorer from Auckland to Wellington, via the Tongariro National Park, and the Coastal Pacific from Picton to Christchurch, via Kaikoura. The Northern Explorer takes about 12 hours, and the Coastal Pacific takes about five. You'll need to book your own InterIslander Ferry tickets. Note that while the Coastal Pacific operates every day, the Northern Explorer only runs three days a week.
Both of these train journeys allow stopovers, so you don't have to make each leg of the journey straight through in one day, but stop at places on the way.