An environment group says a BHP Billiton proposal to transport uranium yellowcake through the Northern Territory should be reconsidered in light of a train derailment near Katherine.

Four carriages left the tracks west of Katherine yesterday and investigators are trying to determine the cause.

Justin Tutty from the No Waste Alliance says BHP's proposal would see a trainload of radioactive material a day on the same rail line.

"We already have yellowcake coming from South Australia, but BHP's proposal is something different," Mr Tutty said.

"We are talking about huge volumes, up to 5,000 tonnes a day, a train movement every day of finely particularised concentrate.

"I don't think the Territory is equipped to deal with a derailment or a collision involving this radioactive material."

He says the group is watching what happens with a Government inquiry.

"We have our eye on the NT Government's inquiry into the transport of dangerous and hazardous materials in relation to the proposal for a nuclear waste dump," he said.

"We are concerned about safety regarding the transport of nuclear waste, but this is a whole new ball game.

"This is far greater volumes, daily movements, and we are talking about a radioactive dust."