Lyttelton's chief fire officer says the port town is like a battlefield.
Mark Buckley told Radio New Zealand two people died on walking tracks hit by rockfalls when the 6.3 earthquake struck on Tuesday but there have been no deaths since.
He says injuries have been minor and the fire service is now helping evacuate elderly people from their homes.
But about 60% of the buildings in the main street have collapsed and most of those still standing are damaged.
Lyttelton was near the epicentre of the quake, 10 kilometres south-east of Christchurch city.
Mr Buckley says the only way in and out of Lyttelton is Dyers Pass Road, through Governors Bay.
The town has no power or water and the Lyttelton Tunnel is impassable. Orion electrical workers are making Lyttelton their top priority as they work to restore power to quake-hit areas.
Mr Buckley says HMNZS Canterbury has provided about 150 personnel and equipment and a fresh water tanker should arrive on Wednesday morning via Dyers Pass Road.
Operations at Port of Lyttelton are suspended while the port company does a full engineering assessment to get a clearer picture of the damage to key infrastructure.
The port says it needs to carry out urgent repair work to its container operations and it may be 10 days before normal operations resume.
It aims to have container operations running on a limited basis in three to four days.
The port says its oil berth operation has held up well but it is checking pipework, and expects it to be operating again by Friday evening.
A tanker is scheduled to arrive on Saturday to discharge fuel.
The port says New Zealand Navy divers have been helping its engineers to assess port structures and carry out soundings to review the channel depth.
There have been no injuries at the port.
Listen to interview with Mark Buckley