Three children rescued from a minivan last week have gone missing alongside their families from an Austrian hospital.

The families were migrants from Syria and were being treated at the hospital for dehydration after they were discovered on Thursday in a minivan with 26 other migrants.

The rescue of the families came just days after 71 bodies were found in a truck on the side of a road in Austria.

A Romanian truck driver was arrested after Austrian police stopped the minivan on the border with Germany, the BBC reports.

Austrian police say when they found the two girls and a boy, aged between one and five years old, and their families they were in a critical condition and almost unconscious.

The families were taken to hospital for treatment and were reported missing overnight.

It's believed the families were trying to cross the border to Germany to escape being deported back to Hungary.

Meanwhile, Austrian experts are performing autopsies on the migrant victims — 59 men, eight women and four children.