The shootings happened shortly after 4.20am on District Road 22 in the district of Kusel, in the state of Rhineland-Palatinate.

The officers - a 24-year-old woman and 29-year-old man - reported via radio that shots were being fired.

"After that, the radio connection was lost," said police spokesman Bernhard Christian Erfort.

"So we don't know what happened.

"Officers were dispatched to the site where they found the colleagues, one injured, one dead."

Two arrested

Two men were later arrested.

One of the suspects, a 38-year-old, will be presented to court in the southwestern city of Kaiserslautern, police said.

They added that he had not given any information.

Another 32-year-old man was detained and police were investigating his involvement in the crime, they added.

Both suspects are Germany citizens, Der Spiegel magazine reported. It added that one of the suspects was a trader of hunted game animals.

Earlier, Mr Erfort said he did not know if the officers had seen something particular about their vehicle that they wanted to check or whether it was just a routine traffic stop.

He did not confirm media rumours that the suspects could have been poachers who were active in the area surrounded by forests and fields.

"For now I have no information on the escape car which is why I can't say whether any game was in the car," he said.

Police have asked the public not to pick up hitchhikers in the district.

Killings 'reminiscent of an execution'

District Road 22 was completely closed off in the Mayweilerhof and Ulmet areas and witnesses who noticed something suspicious were urged to contact the Kaiserslautern force.

The female victim was still studying at a police academy, the GdP police union said.

"Regardless of the motive, this crime is reminiscent of an execution and shows that the police risk their lives for our security every day," interior minister Nancy Faeser tweeted.

She said "we will do everything" to catch the perpetrators.