Key Points:

They stand 73m tall - 8m higher than the Auckland Harbour Bridge - on a ship the size of 2 1/2 rugby fields.

So boaties and North Shore residents could be forgiven for thinking they were looking at a small city on the sea instead of three huge cranes bound for Ports of Auckland.

The three $9 million cranes sit in waiting on the Zhen Hua 11, anchored five nautical miles off Browns Bay. They are due at the Axis Fergusson container terminal early tomorrow morning.

The vessel looks top heavy now - but it dropped three other cranes in Australia on its way here.

Weighing 1250 tonnes each, the cranes were made by the Zhenhua Port Machinery Company on the Yangtze River in Shanghai.

They will be unloaded one by one over five days.

Though the ship may look ungainly and liable to overbalance, it stays upright in high seas by a process known as reballasting.

The ship contains a number of cells that can be filled with water to give it extra stability.

Ports of Auckland corporate communications manager Karen Bradshaw said the new cranes would be the fastest, biggest and most productive container cranes in the country.

Each crane has longer booms and increased lifting power and speed and at full stretch rises to a height of 103m.

The diesel-electric straddle carriers are more efficient, give out fewer exhaust emissions and can be used as generators to power critical re-frigerated cargo in the case of power failure.

Zhenhua Port Machinery Company is the largest container crane manufacturer in the world and can produce up to 125 similar behemoths in one run, with one crane completed every two days.

The 244m Zhen Hua 11 (by comparison the Queen Mary 2, due here in February, is 345m) can raise itself to dock level, allowing an easy transfer of the cranes using a computerised system that allows it to pump water in and out of the hull.