The train was on its way from Hastings to Napier, most movements on the line out of Whakatu being meat or produce, one road transport source said.
No comment was available from Napier Port Co, but the road transport source said the derailment would most likely cause a back-up of carriages rather than any disruption at the port.
Railways enthusiast Ken Le Prou saw the aftermath of the derailment, wondering how the carriages on the bridge might be placed back in the line.
It's at least the second significant closure in a month on the Hawke's Bay line, which is scheduled for reopening by the end of the year to cope with the so-called Wall of Timber from Northern Hawke's Bay and East Coast forestry.
A washout north of Raupunga last month left the track suspended in the air, and KiwiRail assessing what impact it would have on the plans.
A railways enthusiasts' steam train is also scheduled to run north as far as Napier early next month.
The line north of Napier had been closed for more than six years.
It was determined by KiwiRail to be uneconomical with repairs costed at more than $3 million after a major washout left about 100m of track suspended in the air near Mahia on the Wairoa-Gisborne sector in March 2012.
It led to the mothballing of the line, which had been used only for freight trains since Cyclone Bola put an end to regular passenger services in 1988.
The Government, led by Prime Ministers John Key and Bill English, declined support for reopening, but in February the new Labour-led coalition announced a $5m contribution from the Provincial Growth Fund to reopen the line for logging trains to relieve pressure on the highways, work starting almost immediately on reinstating the track to take an estimated 6000 truck trips off the highways.
