Dozens of dead Ethiopian immigrants were dumped on the side of a road in Tanzania after suffocating in a container truck along with many others who survived, in the second fatal human trafficking incident in the country this year.

Up to 45 bodies were dumped along a busy forest highway, the local Guardian newspaper reported on Wednesday, and a further 72 were found alive and taken to hospital.

"When the driver discovered that there were people dying, he decided to throw them in the forest and run away with his vehicle," the paper quoted Deputy Home Affairs Minister Pereira Ame Silima as saying, Reuters reports.

Police in the in the central region of Dodoma, where the bodies were found on Tuesday, declined to comment.

"I haven't seen anything like this ... There were so many bodies lined up along the road. People in passing vehicles were shocked at the sight," said local resident Fatuma Amir.

The east African country is a major transit route for migrants, used by smugglers to ferry Somalis and Ethiopians to South Africa and Europe.

The truck was probably on its way to the south-western border with Zambia and Malawi, officials said. Illegal immigrants are often smuggled by local truckers from Tanzania's commercial capital Dar es Salaam to border towns.

In January, 20 Somali migrants suffocated to death as they were being smuggled in a cramped container truck through Tanzania, their bodies were similarly dumped on the road.

At least 47 people thought to be illegal migrants from east Africa died when their boat capsized in a lake in neighbouring Malawi last Friday.