Police are investigating reports the gunman behind the deadly shooting rampage in Munich lured people to their deaths with a fake Facebook post offering free McDonald's food.

German authorities are examining posts on the social networking site that allegedly asked people to be at the restaurant near the OEZ shopping centre at the time of the shooting, Munich police president Hubertus Andrae told a press conference today.

A gunman identified as an 18-year-old German-Iranian man from Munich opened fire on crowds at the fast food chain before 4pm GMT (1am AEST). He then moved into the OEZ shopping centre.

At least 10 people have been killed in the shooting spree. One of the slain is believed to be the shooter.

There are unconfirmed reports the teenager was shot dead by a plain clothes police officer at the shopping centre. It has also been reported the gunman committed suicide with his body found about 1km from where the massacre took place.

Mr Andraes confirmed children were among those hurt and adolescents had been killed.

Munich police chief Hubertus Andrae attends a press conference in Munich. (AAP)

Details about the “Facebook game” were revealed during a police press conference.

“On Facebook there is a type (of) game whereby at 4pm you should meet in McDonald’s because something… I believe this is a fake game where people are asked to congregate at McDonald’s because McDonald’s might be offering free meals,” one reporter said.

Mr Andrae said police will investigate whether the game may be connected with the crime.

“At the moment it’s simply impossible to say that. It is one part of the rather comprehensive investigation that we are condition with the federal police forces,” he said.

Conflicting reports

Eyewitnesses to the attacks have heard statements from the gunman which offer contradictory explanations as to the motivations for the attack.

Shopping centre bystander Luan Zequiri told German station n-TV he heard the shooter shout an anti-foreigner slur.

The suspected gunman was later filmed shouting "I'm a German".

The scene of the Munich massacre.

But a woman identified only as Lauretta said she was in the bathroom at the McDonald's when she heard the gunman shout "Allahu Akbar".

"I know this because I'm Muslim. I hear this and I only cry," Lauretta said, saying the gunman was targeting children.

"The children were sitting to eat. They can't run."

The Sun pointed out today was the fifth anniversary of white supremacist Anders Breivik's massacre in Norway.

Breivik killed eight people with a car bomb in Oslo before going to a nearby island and gunning down 69 more.

Most of those killed were teenagers at a left-wing youth camp.

Video shows gunman outside McDonald's

Distressing video shows a man dressed in black calmly open fire on a crowd of people outside a McDonald's attached to the Olympia mall.

In the footage, shared widely on social media and broadcast by multiple media outlets, up to 20 individual shots can be heard.

There is no obvious warning the man is about to begin shooting, with crowds milling about unaware until the shooter plants his feet and aims his weapon at a gathering of people.

One woman told Bavarian Radio she was queuing at McDonald's when "panic erupted".

"The staff ran out and all the people followed behind them," she said, according to UK newspaper The Telegraph.

"Children were crying. Everybody running out in panic.

"We heard three shots. Bang, bang, bang."

Other footage appears to show the same man on a rooftop carpark of the mall being abused by the cameraman.

Police escorts evacuated people from the shopping mall (the Olympia Einkaufzentrum (OEZ) in Munich. (AFP)

"You f---ing arsehole," the man filming from a nearby balcony shouts. "F---ing Turks."

"I'm a German," the gunman shouts back.

"Because of you I was bullied for seven years and now I have to buy a gun to shoot you."

People hiding from gunmen in Olympia mall

Many in the Olympia shopping mall hid for hours as police combed the area for more gunmen.

A staff member hiding in the mall, who declined to be identified, told Reuters by phone "many shots were fired".

"I can't say how many but it's been a lot.

"All the people from outside came streaming into the store and I only saw one person on the ground who was so severely injured that he definitely didn't survive."

"We have no further information, we're just staying in the back in the storage rooms. No police have approached us yet."

TV images show dozens of emergency vehicles outside the mall, including police special forces.

Authorities say they have halted several bus, train and tram lines.

The Olympia Mall is the biggest shopping centre in Munich, a city about the size of Adelaide.

Police secures the area of a subway station Karlsplatz (Stachus) near a shopping mall following a shooting in Munich. (AFP)

Second attack in a week

It's the second attack in Germany in less than a week.

On Monday, a 17-year-old Afghan refugee wounded four people in an axe-and-knife attack on a regional train near the Bavarian city of Wuerzburg, and another woman outside as he fled.

All survived, although one man from the train remains in life-threatening condition.

The attacker was shot and killed by police.

The Islamic State group claimed responsibility for the train attack, but authorities have said the teen likely acted alone.

German chancellor Angela Merkel will convene a security council meeting in relation to the Munich shootings.

"Some of you are aware there were shootings in Germany and we don't yet know exactly what's happening there, but obviously our hearts go out to those who may have been injured," US President Barack Obama said.