Some 200 Syrian and Afghan refugees clashed in a crowded German refugee center in Hamburg overnight, leaving four people injured in the third such riot this week, police said Thursday.

Fifty police were called in to contain the mass brawl, which broke out in an argument in a shower block, local newspaper the Morgenpost reported.

A fire and an explosion in a World War II-era bunker injured at least 38 people early Tuesday in the northern German port city of Hamburg.

Firefighters said they would try to douse the blaze with foam to prevent the ignition of about 100 tons of essential oils stored in the bunker which also houses a carpentry workshop.

Former SS officer Oskar Groening, dubbed the "bookkeeper of Auschwitz", asked for "forgiveness" over his role in mass murder at the Nazi death camp, as his German trial began Tuesday.

"For me there's no question that I share moral guilt," the 93-year-old former Nazi told the judges, admitting that he knew about the gassing of Jews and other prisoners.

Police have released two suspects detained after the firebombing of a German tabloid that published cartoons from the French satirical paper Charlie Hebdo mocking the Prophet Mohammed, officials said Monday.

The two men, aged 35 and 39, were picked up in the northern port city of Hamburg soon after the early-morning attack on the regional daily Hamburger Morgenpost Sunday, which caused only minor damage.

A German tabloid that reprinted cartoons from the French satirical paper Charlie Hebdo lampooning the Prophet Mohammed was targeted in firebombing Sunday, police said. 

With security services on high alert after a killing spree in Paris by Islamic extremists, police in the northern German port city of Hamburg said no one was injured in the blaze at the headquarters of the regional daily Hamburger Morgenpost, which caused only slight damage. 

Bayern Munich goal-scorer Arjen Robben has said the Bavarian giants are hitting top form after they demolished Hamburg 5-0 in the German league.

After a faltering start to the season, Bayern produced an impressive display on the third weekend of the Bundesliga campaign on Saturday as Robben and fellow star winger Franck Ribery ran the Hamburg defense ragged.

In Germany the idea of a teenager spending a few months abroad looking after someone else's children while she studies or travels has given rise to a new concept -- the granny "au pair".

Newspapers now explicitly solicit applications from older women rather than students with ads such as: "Family living in Australia with two children aged 4 and 2 seeks German replacement granny for three to six months".