St John confirmed the death of a man in the 5pm explosion.
"We did not transport any patient from the scene - one person was deceased at the scene," St John spokesperson Ian Henderson said.
The Herald understands Maritime New Zealand will board the ship todayu at 10am to carry out an investigation.
Preliminary reports that nobody was injured were incorrect, Port Otago chief executive Geoff Plunket said.
"There was a loud explosion on board and a gas cylinder appears to have exploded. It is a very serious incident."
Australian passenger Krystal Friggieri told the Herald she was on deck 11 when the explosion happened.
"It was pretty loud. All I saw then was the gas bottle spinning on the [wharf]."
She said the captain of the ship told the passengers via the intercom a crew member had died.
"He's been keeping us informed. Everyone's a bit upset."
She believed the explosion was on deck seven, which was cordoned off to passengers.
She said police were still on the ship.
The explosion was at the stern of the 113,000-tonne ship, which can carry 3082 passengers.
People were on the wharf at the time but no one was injured.
Carnival Australia spokesperson David Jones confirmed a crew member was killed in the explosion.
"First reports indicate that the incident happened during some technical work on the hydraulic launching system on a tender vessel," he said.
"We are deeply saddened that a member of Emerald Princess' crew was fatally injured."
He said the company, which operates the cruise ship, was working closely with police and other authorities and assisting in their response and inquiries.
He said Emerald Princess is on a 12-night round trip cruise from Sydney to destinations in New Zealand.
He added no passengers were injured and the ship won't leave port until it is permitted to do so.
Maritime Union Port Chalmers-Dunedin secretary Phil Adams said he was working in the port's control room when he heard a "massive explosion''.
"I got up and I saw this pipe or a tube lying on the wharf. It was a gas cylinder, by the sounds of things, that had just blown straight off the ship and on to the wharf.
"Man, I've never heard an explosion like it in my bloody life. I'd say most of Port [Chalmers] felt it.''
He did not see a fireball, and there were no obvious signs of damage on the cruise ship.
His first thought, upon hearing the explosion, was terrorism. "But it's certainly not that.''
"It's quite sad, really, that something like this has happened at our port.''
The cruise ship had been due to sail at 6pm, but had been delayed as passengers returning from the city were kept back from the wharf following the explosion, he said.
Some were now being allowed to board the vessel, but it was not yet known when it would depart.
The noise of the explosion garnered attention on social media with people reporting hearing the explosion from as far afield as Sawyers Bay, about 2km from the port.
"Sounded like a container fell,'' one commenter said.
Emerald Princess made her maiden arrival to New Zealand on November 18 and cruised through Fiordland National Park.
The cruise ship has also visited Akaroa, Picton, Napier, Tauranga and Auckland.
- With Otago Daily Times
