Newshub understands the train derailment in Auckland's Britomart on Wednesday morning may have been caused by potentially faulty Chinese steel.

The derailment caused a huge mess, both for passengers on board at the time and with severe delays due to the clean-up affecting others.

KiwiRail chief operating officer Todd Moyer confirmed to Newshub there is Chinese steel in the Britomart tracks, along with other kinds of steel.

The company said it can't rule out Chinese steel being used at the point the train came off the tracks, but it needs to see what comes out of the investigation.

The union representing steel workers has long held fears about the quality of steel imported from China.

"For some time I've highlighted that I believe that there are quality issues, and there's no checks and balances with the quality of the steel that's coming into New Zealand," E tū union spokesperson Joe Gallagher told Newshub.

E tū is also concerned about the use of that steel on railway tracks.

"It's a major concern, I mean you know you're talking about people being transported, the general public being transported, on these railways," Mr Gallagher said.

"We're talking about shifting our freight. We've only just rebuilt Kaikōura. We can least afford to have another major derailment."

Chinese steel was also used in Te Matau ā Pohe bridge in Whangarei; the entire opening section is made with it.

Four years after it was opened, with much fanfare, the bridge had to undergo major maintenance and some of the Chinese steel was cut out.

The Whangarei District Council told Newshub some of the steel edge was cut off so the bridge can expand during summer.

A source familiar with the Britomart derailment told Newshub when trains derail it's often at the railroad switch point, but usually at the thinner blade end.

But they said in Britomart it was a crack at the opposite, thick end - something that is highly unusual.

Newshub.