A Syrian man has killed himself and wounded 15 others in a suicide bombing at a German music festival.

The incident at the Ansbach festival was described as an "Islamist" attack by Bavarian interior minister Joachim Herrman. He said the man had pledged allegiance to Islamic State on a video found on his mobile phone.

"A provisional translation by an interpreter shows that he expressly announces, in the name of Allah, and testifying his allegiance to [Islamic State leader] Abu Bakr al-Baghdadi...an act of revenge against the Germans because they're getting in the way of Islam," Joachim Herrmann told a news conference.

"I think that after this video there's no doubt that the attack was a terrorist attack with an Islamist background."

Islamic State claimed responsibility for the attack, according to Amaq, a news agency that supports Islamic State.

The attack, outside a music festival in Ansbach, a town of 40,000 people southwest of Nuremberg that has a U.S. Army base, was the fourth act of violence by men of Middle Eastern or Asian origin against German civilians in a week.

The man, whose identity has not been released, was a 27-year-old asylum seeker who had arrived in Germany two years ago and had been in trouble with local police repeatedly for drug-taking and other offences. He had been in treatment after twice before trying to kill himself. 

"It's terrible...that someone who came into our country to seek shelter has now committed such a heinous act and injured a large number of people who are at home here, some seriously," Herrman told a hastily convened news conference earlier on Monday.

"It's a further, horrific attack that will increase the already growing security concerns of our citizens. We must do everything possible to prevent the spread of such violence in our country by people who came here to ask for asylum."

He told Reuters the recent attacks raised serious questions about Germany's asylum law and security across the country and said he planned to introduce measures at a Bavarian government meeting on Tuesday to strengthen the police forces and ensure they have adequate equipment.

US sources said the bombing did not appear to be a well-planned operation and could well turn out to be the act of another deranged individual.

Herrmann said the man had been denied entry to the Ansbach Open music festival shortly before detonating the bomb outside a restaurant called Eugens Weinstube.

More than 2,000 people were evacuated from the festival after the explosion, police said. A large area around the blast site remained blocked off hours later.

Ansbach resident Thomas Debinski said people panicked when they heard the explosion, especially after the events of the past week.

"Suddenly you heard a loud, a really loud bang, it was like an exploding sound, definitely an explosion," he said. "[People were] definitely panicking."

Debinski said it soon became clear that someone had set off a bomb in a rucksack.

Earlier on Sunday, a 21-year-old Syrian refugee was arrested after killing a pregnant woman and wounding two people with a machete in the southwestern city of Reutlingen, near Stuttgart.

"After what just happened in Munich, and today in Reutlingen, what you hear about, it is very disturbing, when you know that such a thing can happen so close to you, in such a small town as Ansbach," Debinski said.

A week ago a 17-year-old who had sought asylum in Germany was shot dead by police after wounding five people with an axe near Wuerzburg, also in Bavaria. He was initially thought to be Afghan but federal Interior Minister Thomas de Maiziere has since said he may have been from Pakistan.

Police said neither Sunday's machete attack nor Friday's shooting in Munich bore any sign of connections with Islamic State or other militant groups.

Islamic State claimed responsibility for the Wuerzburg attack as well as the July 14 rampage in the French Riviera city of Nice, in which a Tunisian man drove a truck into Bastille Day crowds, killing 84 people.

Additional reporting by Reuters.