Colleagues of a man killed while working on Wellington's south coast today say they are traumatised by his death.

The man was replacing a transmission line at the remote Transpower site at Oteranga Bay, south of Makara, this morning, when the cherry-picker machine he was on fell over.

Another worker was seriously injured and was flown to Wellington Hospital with fractures to both legs as well as broken ribs, and a bruised or collapsed lung.

The two men were tethered to a basket, so were not thrown clear when the machine toppled.

Both men were from Palmerston North and worked for Electrix.

Electrix general manager Robert Ferris told NZPA the company was devastated by the tragedy.

"We're working with both the team members plus the families of the two men involved and we're providing all the assistance we can to help them through this.

"We have an employee assistance programme, so that's been made available to the team members because obviously they've been traumatised by this event."

The Department of Labour is investigating the incident as is Transpower. Police were talking to 12 witnesses.