Italian authorities are still trying to identify all of the 21 victims of Tuesday's deadly bus crash in Venice.

The electric bus crashed through a bridge barrier, and plunged almost 15m (50ft) in the mainland borough of Mestre, before bursting into flames.

DNA samples are being used to confirm the identities of those who were not carrying personal documents, prosecutor Bruno Cherchi said.

Three children including a baby were among the dead, according to officials.

The bus was carrying 39 tourists from the centre of Venice to a campsite. On Wednesday evening, relatives began arriving in Italy from other countries to identify the dead.

Mayor Luigi Brugnaro said a huge tragedy had taken place. "An apocalyptic scene, there are no words," he said on social media.

CCTV footage showed the vehicle driving past another bus before toppling off the carriageway.

One rescuer spoke of a "tragedy of young people, if not very young people, except for a few adults".

Nine Ukrainians, three Germans, four Romanians, two Portuguese, a South African national and the Italian driver were among those killed, a spokesperson for Venice's mayor said.

Fifteen people are known to have been injured, five of them seriously - including Ukrainians, Austrians, Spaniards and other foreign tourists, according to officials.

Among the injured were two 16-year-olds and two younger children, the local governor said.

Two German brothers, aged seven and 13, were being treated for broken bones in hospital in nearby Treviso. Their parents were killed in the accident and the boys were being given counselling.

A young Croatian woman who was on her honeymoon also died, Ansa news agency reported. Her husband of about three weeks was sent to hospital.

Some survivors in the Angelo di Mestre hospital were asking for their loved ones, said the head of medicine, Chiara Berti. "There were entire families, grandparents, grandchildren, spouses."

Venice prosecutor Bruno Cherchi said only three or four survivors had so far been able to talk to investigators by Wednesday afternoon.

The city's authorities have declared three days of mourning after the tragedy.

The bus crashed at around 19:45 (17:45 GMT) on Tuesday. It had apparently been rented by a local company to pick up tourists from the historic centre of Venice and take them to a campsite in the nearby Marghera district, on the mainland.

Witnesses saw the bus scraping along the guard-rail on the flyover for 50m, before tumbling to the ground, the prosecutor added. BBC