At least four Russian tourists were killed after their bus overturned in northern Greece on Friday, Russian officials said.

The bus was carrying 49 tourists from their hotel to the airport when it crashed on a highway near the country's second city, Thessaloniki, in the early hours of Friday morning.

The crash also injured some 30 Russian tourists, a diplomat at the Russian consulate in Thessaloniki said.

The Greek authorities are investigating the crash.

It is reported to be one of the country's worst traffic accidents in more than a decade.