BERLIN (AP) — A bus carrying German seniors on holiday slammed into the back of a truck that had slowed for a traffic jam and burst into flame Monday, killing 18 people on a major highway in Bavaria, authorities said.

More than two dozen people who were hurt escaped the bus before it became fully engulfed in fire, police said. By the time the blaze was put out, only the vehicle's charred, twisted frame remained.

The bus from the eastern state of Saxony rear-ended the trailer-truck on the A9 near Muenchberg, north of Nuremberg and not far from the Czech border. Of the 30 people injured, at least two were reported in life-threatening condition, authorities said.

"After we got there, nobody else got off the bus," Muenchberg firefighter Andreas Hentschel told the dpa news agency.

The accident occurred at around 7 a.m., when there was no rain and visibility was good. The investigation, which included prosecutors, was looking into what type of cargo the truck was hauling, police said.

The bus driver was among the dead. The truck driver was not injured, police said.

The rest of the fatalities were men and women between 66 and 81 years old, police said.

A total of 48 people were on the bus, including two drivers. The passengers were primarily from Saxony.

Some 200 first responders rushed to the scene, and five helicopters whisked the injured to nearby hospitals. Simple wooden coffins were wheeled in for the remains recovered from the bus.

When firefighters first arrived, the fire was so hot that they could not get anywhere close to the burning bus to rescue those stuck inside, Transport Minister Alexander Dobrindt told reporters at the crash site.

"All they could do was extinguish the fire," he said. The heat was so intense that it destroyed the entire bus and everything inside except for the steel frame.

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Associated Press Writer David Rising contributed to this report.