Berlin (CNN) -- A string of arson attacks has hit the German capital, with vandals burning dozens of cars this week, including an additional 11 overnight, authorities said Friday.
At least 50 cars have been torched since Monday, authorities said.
Authorities described 30 crimes are "politically motivated," with police spokesman Guido Busch saying Friday that the motive has changed during the week.
"While the first attacks were concentrated on the district of Charlottenburg, more and more copycats are now trying to imitate the arson attacks in various other parts of the city," Busch said.
The vandalism has heightened fears in normally quiet, gentrified districts of Berlin.
"In my opinion, it is vandalism, and we must hope that the offenders don't cross the line to terrorism," Dieter Wiefelsputz, a home affairs expert for the German Social Democratic Party, said Thursday.
German police say they still have no clear idea who the perpetrators are. They are offering a 5,000-euro reward, just over $7,000, for any leads that might result in arrests.
A government official said the attacks are unprecedented.
"Right now, we have reached a new peak of arson attacks in Berlin," said Ehrhart Koerting, the senator for domestic affairs who's responsible for Berlin's police force.
'I don't know what's going through the heads of the people doing this," he said.
The founder of a website called "burning cars in Berlin" believes that class envy is the reason for the attacks.
The website, which is run by the CEO of a travel company, documents incidents across the city.
"The burning mostly occurs in districts like Kreuzberg, Berlin Mitte or Friedrichshain. Its inhabitants don't like their rich neighbors, so they set their cars on fire," said Uwe Frers, who runs the website.
Berlin neighborhoods have been transformed in recent years as wealthy people move into areas that used to have high unemployment, and low housing and living costs.
But German sociologist Klaus Hurrelmann says the motivation for the attacks has changed over time.
The attacks now are dominated by "youngsters who are searching for the London kick," he said.
"Setting cars on fire is cheap and easy," said Hurrelmann, a professor at the University of Bielefeld.
The vandalism has found its way into modern culture.
In his song "Cars are burning," Frankfurt-based rapper Real Jay asks: "What are you going to do, when the cars are set on fire?"
At least 135 cars have been torched this year, compared with 54 in 2010, authorities said.
"Right now there are about 100 extra police officers out on the streets of Berlin each night to arrest the attacker or attackers," police spokesman Thomas Neuendorf said.
Despite the large police presence, Busch said it will be hard to contain the crimes.
"Even if we would have 1,000 extra police staff out on the streets, we couldn't stop the offenders from burning cars. Berlin is just too large," Busch said.