The death of a Lyttelton port worker is further evidence of the need for an urgent inquiry into port safety, unions say.

The Lyttelton Port Company worker was killed on a ship that was being loaded with coal for export at Cashin Quay on Monday morning.

Maritime New Zealand is investigating the death, which is the second at the country's ports in less than a week.

Stevedore and father of two Atiroa Tuaiti, 26, fell to his death while working on a ship at the Ports of Auckland on Tuesday. His father was working there when the tragedy unfolded.

Council of Trade Unions president Richard Wagstaff says the Lyttelton worker's death is a tragedy and serves to reinforce calls for an inquiry, from which national standards could be developed.

"Every worker deserves to know that when they go to work in the morning, that they will be coming home safely at the end of the day. Sadly that is currently not the case in this industry, and urgent action is needed."

Maritime Union national secretary Craig Harrison says the deaths were preventable.

"We've got a terrible record in the industry in the last few years.

"It's not a big industry, and if you compare us to the Australian steel and mining industries which have far greater volumes and not anywhere the fatalities or harm we seem to be facing."

Workplace Relations and Safety Minister Michael Wood last week said he did not accept that workplace deaths were inevitable. He has not ruled out a national inquiry into injuries and deaths at New Zealand ports, and told RNZ he would consider a union proposal.

"While it is too early to determine what has occurred, I know people will be rightly concerned about the safety culture at our country's ports.

"Two incidents in a week is unacceptable and in the coming days I will confirm what further steps the government will take to minimise future harm at our ports."

Lyttelton Port Company acting chief executive Kirstie Gardener issued a statement confirming the worker's death.

"At the moment we can't confirm any further details on the incident. I wish to express my deep sadness and condolences to both the family of our team member and to the rest of the LPC team.

"Our focus right now is on supporting our staff and the family of our LPC team member at this tragic time."