Firefighters are seen at the site where a coach burst into flames after colliding with a truck on a motorway near Muenchberg, Germany, on Monday. [Photo/Agencies]

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

Some 200 emergency crews were at the scene and helicopters whisked away the injured to nearby hospitals. Simple wooden coffins were wheeled in for the remains recovered from the blackened, twisted wreckage of the bus.

Chancellor Angela Merkel thanked the emergency crews involved and sent the government's transport minister, Alexander Dobrindt, to the scene.

"Our thoughts are with the families of the victims and we wish all those who were injured a speedy recovery," she said.

Authorities said forensic specialists were being brought in from Germany's federal police office to remove and identify bodies from the charred vehicle. Police spokeswoman Irene Brandenstein said the work was labor intensive because the bus was so badly damaged by the fire.

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

The accident took place around 7 am 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 accident led to long traffic jams on the A9, the main thoroughfare from Berlin to Munich. 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.

It was not immediately clear what caused the initial traffic jam.

Two drivers and 46 passengers were on the bus, Brandenstein said. It was not known if the person driving the bus at the time was dead or alive.

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

Police said the group on the bus was seniors from Saxony in eastern Germany. The German news agency dpa reported that all passengers were Germans.

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

If those missing are confirmed killed, the accident at the start of the summer holiday season would be one of the worst to hit Germany.

Among the deadliest in recent years was a collision in June 2007, when 13 people were killed as their tour bus drove off the road and plunged several meters down a slope in eastern Saxony-Anhalt state.

Across Europe, the last such accident struck on Jan 21 in Italy, when an accident involving a Hungarian bus carrying teenagers left 16 dead.

CHINA DAILY/AFP