Prime Minister Enrico Letta will join bereaved relatives at a mass funeral Tuesday for the 38 people killed in Italy when a coach plunged off a viaduct near Naples.

Prosecutors have launched an investigation into possible manslaughter over Sunday's accident, the worst such crash in western Europe in the last decade.

Hundreds of relatives had to spend agonising hours viewing bodies and identifying victims on Monday before the victims were carried off in flower-covered coffins.

The bereaved families are expected to attend Tuesday's funeral in a vast sports hall near the town of Pozzuoli.

The coach, carrying 48 people including children, rammed several cars after failing to break on a bend, smashing through a crash barrier and off the viaduct to plunge 30 metres (98 feet) down.

By late Monday evening, the dead had been laid out in state in the concrete and glass sports hall, ready for Tuesday's mass, which begins at 0730 GMT.

Prime Minister Enrico Letta, who announced a national day of mourning for Tuesday, said he would attend the funeral with the lower house of parliament speaker Laura Boldrini, according to Pozzuoli mayor Vincenzo Figliolia.

On Monday, hearses lined up at a school near the crash site which had been turned into a temporary morgue.

Sobbing relatives clutched at the coffins as they were taken away or collapsed into the arms of Red Cross workers.

Earlier, officials had called out the names of each family from a list and the relatives put white masks over their mouths to enter the makeshift morgue.

"They told me to look at all the bodies until I found my brother," said one man who gave just the name Ciro.

"It was like a mountain had fallen on my head," he said of the search for his 40-year-old sibling.

The group on the coach was returning from a pilgrimage to Pietrelcina in the Campania region, the birthplace of Padre Pio, an Italian priest canonised in 2002 and worshipped in the country's south.

Ten passengers were injured in the accident, along with another nine people in cars hit by the coach before it crashed off the highway.

While rescuers were quick to remove the shattered coach from the wooded area off the highway, passenger belongings streaked with blood -- including shoes, books and a torn teddy bear -- still lay strewn on the ground.

The crash happened in an area known as an accident black spot.

The manslaughter probe will look into the possible role of the driver as well as the state of the coach and the crash barrier on the highway.

The coach crash was the deadliest in western Europe in the last decade and the worst in Europe since an October 2010 accident in Ukraine when 45 people died.

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