At least four German security guards working for a private firm are being investigated over the repeated abuse of asylum seekers.

Several photos and a video have surfaced, showing incidences of ill-treatment of refugees, at a centre in Burbach in the west of the country. One image shows the foot of a German security guard pressed against the neck of an Algerian asylum seeker.

Police raided the centre and questioned guards and refugees after a local journalist received a DVD showing the abuse.

At least two of the four guards are understood to have previous criminal records for drug abuse and violence.

European Homecare, which runs the centre, is one of the biggest private companies operating centres for asylum seekers in Germany. Renate Walkenhorst, a spokesperson for the company, said they didn’t always have time to check who works for them.

“Sometimes you are forced to hire people who you you’re not 100 percent sure about from the beginning, who you have to keep an eye on. That’s a fact, because we had four days to set up the Burbach shelter,” she said.

Authorities say the rising numbers of asylum seekers in Germany has put a strain on security companies.

Germany has seen a 50 percent increase in applications compared to a year ago, largely driven by the wars in Iraq and Syria.

Human rights groups in Germany say they fear aggression towards asylum seekers is on the rise.