Ferguson riots
Demonstrators protest the shooting death of teenager Michael Brown in Ferguson, Missouri Getty

Two journalists were arrested in a McDonalds in Ferguson, Missouri, amid demonstrations over the shooting of an unarmed black teenager by an officer from the town's predominantly white police force.

Ryan Reilly, of the Huffington Post, and Washington Post reporter Wesley Lowery tweeted their arrest live from the fast-food restaurant.

The reporters said they were assaulted and detained after filming officers inside the restaurant and not leaving fast enough when ordered out.

Reilly stated that an officer grabbed his belongings, forced them into his bag and arrested him, using his finger to create a pressure point on his neck before aggressively forcing him against a wall.

"The worst part was he slammed my head against the glass purposefully on the way out of McDonald's and then sarcastically apologised for it," he said, as reported by the Wire.

The Huffington Post condemned the detention of Reilly as "militant aggression", while the Huffington Post said the incident was an "assault on the freedom of the press to cover the news".

The news came as groups of protesters, demonstrating over the killing of 18-year-old Michael Brown, were confronted by armed riot police firing teargas and rubber bullets.

Officers armed with assault rifles advanced towards the predominantly African-American crowds with armoured vehicles, after two glass bottles were thrown at them in a relatively peaceful protest.

A camera crew from al-Jazeera America said they were shot with rubber bullets.

Another reporter at the scene, Matt Pearce of the Los Angeles Times, stated the Ferguson police chief was shocked when he heard that two reporters had been arrested.

"I told them to release them," the chief told Pearce, referring to the riot command. He added that Reilly and Lowery were likely detained "by somebody who didn't know better".

The White House said early on Thursday that Barack Obama had been briefed by the US attorney-general, Eric Holder, on the escalating clashes between police and demonstrators.

Protesters were angry at the shooting of Brown on Saturday afternoon by a Ferguson city police officer and the response by authorities. According to the police, the shooting followed an assault on an officer, but a friend walking with the teenager said the 18-year-old was grabbed after declining a request to move onto the pavement.

The witness said Brown was then repeatedly shot as he tried to run away. The officer involved has not yet been named and St Louis County police are investigating.