Eighteen people are feared dead after a bus carrying a group of German senior citizens crashed into a truck on a highway in Bavaria and burst into flames, police said.

Thirty people were injured in the early-morning accident, some seriously, while 18 still considered missing “are believed to have died on the burning bus”, police said in a statement.

Authorities said that forensic specialists were being brought in from Germany’s federal police office to remove and identify the bodies from the charred vehicle.

Police spokeswoman Irene Brandenstein said the work was slow and labour-intensive given how badly damaged the bus was by the fire.

“The investigation of the accident is very complex and time-consuming,” Ms Brandenstein said.

Smoke rises from a coach after a crash on the motorway in Germany.

The accident took place around 7am (local time) when the bus rear-ended the trailer-truck at the end of a traffic jam on the A9 highway near Muenchberg in Bavaria, not far from the Czech border.

The highway remained closed on both sides for hours and police tweeted later that the road leading south would be shut down for the entire day.

Several helicopters, firefighters and ambulances were on the scene to rescue the injured.

Two drivers and 46 passengers were on the bus, Ms Brandenstein said.

By the time firefighters arrived and extinguished the flames, the bus was a black, smoking skeleton.

Police said the group on the bus came from Saxony in eastern Germany and there were no children were on the bus.

The German news agency dpa reported that all passengers were German citizens.

A phone number was activated to provide family members with information.

Ms Brandenstein had no immediate information on the condition of the truck driver.

The accident led to long traffic jams on the A9, which is the main thoroughfare from Berlin to Munich.