More than 24 hours after a massive train crash, rescuers in Tanzania were still struggling to pull victims from the wreckage.

Officials say as many as 200 people were killed and up to 800 injured when a train lost power on Monday morning and rolled backwards down a slope, colliding with a goods train and derailing.

"There are bodies that are still piled up inside the wagons," Deputy Health Minister Hussein Mwinyi said.

The crash happened at Igandu, near the administrative capital of Dodoma, about 400 kilometres west of Dar es Salaam.

Overwhelmed emergency services have set up a makeshift morgue in a sports stadium, laying out the dead for identification.

Some of the train's carriages have been crushed beyond recognition.

The ground near the crash is littered with personal belongings: luggage, shoes, schoolbooks. Soldiers using plastic bags for gloves are sifting through the wreckage looking for body parts.

Frantic relatives

And at the main hospital in Dodoma, officials closed the entrance as frantic relatives crowded in to demand news of their loved ones.

More bodies were trapped inside

"I need to see if my brother is alive," Asha Mohammed told Reuters.

Many of the estimated 1,000 passengers on the overcrowded train were trapped inside the wreckage for hours.

As darkness fell on Monday night, some were still crying out for help from inside the mangled train, Betty Mkwasa, a reporter with Independent Television told the Associated Press.

Crews were using cranes on Tuesday to try and lift the carriages as they searched for survivors or bodies.

We are trying, we are doing our best but we are stretched with little equipment

Dr Jacob Chembela

Mourning period

Prime Minister Fredrick Sumaye has declared two days of national mourning, with all flags to be flown at half mast on Tuesday and Wednesday.

Isaac Mwakajila, assistant director-general of Tanzania Railways Corporation, said the train had suffered a mechanical fault on the hill.

"The train went off the railway tracks backwards and smashed into another train behind it going in the same direction. It had 22 cabins and 21 of them fell off the rail tracks," he said.

Witnesses said the driver of the passenger train and several passengers leapt off as it hurtled down the incline.

Hospital overwhelmed

Many of the injured were transferred to Dodoma hospital where the doctor in charge, Jacob Chembela, said the situation was desperate.

"We are receiving more people... we are trying, we are doing our best but we are stretched with little equipment," Dr Chembela said.

The way the coaches are piled on top of each other, from far away you would think it is a multi-storey building

Prime Minister Frederick Sumaye

Health Minister Anna Abdallah said that a plane carrying doctors had flown from Dar es Salaam to Dodoma.

Ms Abdallah, who is herself a doctor, helped to treat the injured.

Parliament was in session in Dodoma at the time of the crash and Prime Minister Frederick Sumaye went to the scene along with the Minister of Transport, Mark Mwandosya.

"The way the coaches are piled on top of each other, from far away you would think it is a multi-storey building," Mr Sumaye told parliament after visiting the scene.