The resources necessary to invade New Zealand would be considerable. New Zealand is roughly 5,000 nautical miles from any potential Asian invader. New Zealand has an area of 268,021 square kilometres with a population of 4.6 million people. There are an estimated 1.1 million firearms, mostly civilian hunting rifles.
The only equivalent military operation in history was the Falklands/Malvinas campaign in 1982. The British task force eventually comprised 127 ships sailing 6,830 nautical miles from Southampton to the Falklands. The financial cost of the campaign at the time was UKP2.778 billion ($20.19 billion New Zealand 2016 dollars) including the replacement cost of war damaged ships and equipment. This does not include the whole of life costs of injuries to service personnel.
The Falkland Islands has an area of 12,200 square kilometres with a population of 2,932 people of British (i.e. friendly to the invader) ancestry.
The forces deployed in the Falklands were:
Land forces: More than 10,000 men. All professional soldiers from elite units.
Navy: 2 aircraft carriers, 5 submarines of which 4 are nuclear, 8 destroyers, 15 frigates, 2 assault vessels, 4 landing crafts, a hospital boat, 3 ambulance boats, 7 mine-sweepers, 11 refuelling tankers, 1 helicopter support vessel, 5 cargo supply boats, 1 patrol boat, the HMS Endurance.
Requisitioned ships: QE2, Canberra and 47 other vessels (tankers, cargoes and ferries)
Air forces: 34 Harriers, 200 helicopters, plus Vulcan bombers operating from Ascension Island.
The Argentinian occupation force was composed of 12,978 men, principally badly trained young recruits with 18 105mm artillery guns
Air force: 78 A4 Skyhawks, 24 Dagger, 18 Mirage, 5 Super Etendard, 6 Canberra, 144 Puccara, 9 Hercule C130.
D-Day involved 156,115 allied troops, 6,939 vessels: 1,213 warships, 4,126 landing craft of various types, 736 ancillary craft, and 864 merchant vessels. There were no aircraft carriers involved as the sea gap was only 40km.
The invasion of Iraq required 160,000 troops to cover a country of 437,072 square kilometres and a population of 37 million. This BBC site shows that the war cost the United States US$801.9 billion, 4,487 deaths, 32,000 wounded. The war killed at least 100,000 Iraqis and lead to a population divergence from previous trends of 650,000.
Assuming China has sufficient soldiers its real problem is getting them to New Zealand. The Chinese People's Liberation Army Navy Surface force operates
1 aircraft carrier. It is building 1 more and had plans for another 2
4 amphibious transport docks (Type 071 amphibious transport dock ) able to carry 800 troops and 20 armoured vehicles
with sufficient range to reach New Zealand
1 hospital ship
5 troop transports (with insufficient range)
17 fleet replenishment ships
3 large transport ships (insufficient range)
Comparing Chinese naval resources with those of Britain in 1982 it appears the Chinese could only attack New Zealand if
1) China committed all its sea forces to attacking us and
2) all our erstwhile allies ignored the Chinese task force
In fact China is far more likely to act on its claim on the island of Taiwan which it regards as part of China and is only 130km away. The fact that no Chinese leader has attacked Taiwan suggests that China is not (as yet) a significant threat. This report says the People's Liberation Army is not capable of invading Taiwan
Similarly Indonesia has plenty of manpower but not enough shipping
4 amphibious transport docks
10 ocean going landing ships
Which might be enough to monster a small island but can't deliver enough men to take over a country this size.
There is zero chance of an armed invasion of New Zealand by China or Indonesia within the foreseeable future.
Threats to NZ >