Munich, Germany: In the chaos sparked by the Munich mall shooting, city residents spontaneously opened their doors to people unable to get home -- a move hailed for its courage and solidarity.

Almost as soon as police shut down Munich's entire public transport system on Friday evening in an effort to prevent suspects from slipping through their net, people took to social media to offer a roof to anyone stranded.

Under the hashtag #offenetuer ('open door'), anyone who found themselves with no safe place to go to could seek refuge until the transport network was back up and running -- an approach also seen in France after the Paris and Nice attacks.

"We have beer and a place to sleep near Prinzregentenplatz/Max Weber Platz. DM me!" tweeted one user, @JoTaucher.

Munich, Germany's third-largest city, was reeling Saturday after an 18-year-old German-Iranian student killed nine people and injured 19 others in a busy shopping mall, before committing suicide.

Initially there had been reports of three possible attackers, but by Friday night police had ruled that out and said the shooter acted alone.

The generosity of people's response to the attack found immediate praise among the authorities.

"How Munich's population reacted, the initiatives that were there to offer people protection and help, this solidarity impressed me deeply. It was a good sign of a civil society," Bavaria's finance minister Markus Soeder told a news conference.

"Amongst all the shock and mourning, there is still hope."

The local daily Abendzeitung was similarly moved.

"On an evening where the city descended into panic and Munich's population fled in sheer terror from public spaces, restaurants and beer gardens, a great many spontaneously offered them refuge," it wrote in a leader column.

A young woman who gave her name as Tamara told AFP that she and her family were shopping in the OEZ mall when the shooting began.

She and her Turkish husband, with their two children aged two and four, found themselves with nowhere to go because the nearby street where they lived had been cordoned off.

"We'd been shopping at C&A. We didn't actually hear any of the shots fired," Tamara said.

"It all happened so quickly. We only realised what was going on when we saw the TV reports. We were ordered to leave the mall as quickly as possible and we first thought it was a false alarm," she explained.

"But then we saw everyone else running, too."

When the young family realised they could not go home, they took shelter in a nearby tower block.

"We got into the lift and rode up to the 14th floor and rang on the doorbell. There was a pram in front of the door, so we thought, OK, if someone's going to open the door, it'll be another family. We've got children, too, as you see. But we didn't know them."

The family invited them in and let them stay.

In the city centre, hotels also offered shelter to anyone stranded, allowing them to remain in the lobby if all the rooms were booked.

The OEZ mall was still heavily cordoned off on Saturday as forensic experts continued to scour the site for clues.

Crowds of onlookers mingled among a mass of television crews and journalists at the police line.

But people were already laying flowers and lighting candles next to the mall for those killed or injured during the shooting.

One hand-written placard asked simply "Why?".

Another bystander, a 78-year-old Hungarian man who gave his name as Meszaros, said he had lived in the area for more than 40 years.

"What goes through the mind of someone like that," he asked. "What are his friends and family feeling and thinking?"

He had heard reports that the 18-year-old gunman had dual German and Iranian nationality.

"That means he grew up here. Did he just flip or were there political reasons?" Meszaros asked.

"Nothing like that has ever happened here before. It's inconceivable."