A man who said he was investigating a conspiracy theory about Hillary Clinton running a child sex ring out of a pizza place has fired an assault rifle inside the Washington DC, restaurant injuring no-one, police and news reports said.

Metropolitan Police Department spokeswoman Aquita Brown said police received a call Sunday afternoon (local time) about a male with a weapon on Connecticut Avenue, in an affluent neighbourhood of the nation’s capital.

Edgar Maddison Welch, 28 of Salisbury, North Carolina, walked into the front door of Comet Ping Pong and pointed a firearm in the direction of a restaurant employee, the Washington Post reported.

The employee was able to flee and notify police.

Mr Welch then fired the gun into the floor before police responded and arrested him without incident.

Two firearms were recovered inside the restaurant and an additional weapon was recovered from the suspect’s vehicle, police said in a statement on Sunday evening.

Mr Welch was charged with assault with a dangerous weapon.

The Comet Ping Pong is in a neighbourhood of well-tended private homes and apartment buildings on leafy streets that lead to a mix of shops, restaurants and the Politics and Prose book store.

The restaurant gained notoriety during the presidential campaign after fake news stories stated that Ms Clinton and her campaign chief ran a child sex ring out of the restaurant, The New York Times and other news organisations have reported.

Mr Welch told police he had come to the restaurant to “self-investigate” the fictitious online conspiracy theory, which spread online during Mrs Clinton’s run for the White House, the police statement said.

Ms Clinton was the target of multiple fake news stories during the campaign. Photo: Getty

The Comet, its owner, staff and nearby businesses were caught up in an onslaught of conspiracy theories and fake news during the often contentious presidential campaign and were the victims of social media attacks and death threats, the Post reported.

James Alefantis, owner of Comet Ping Pong, released a statement late Sunday night that denied what he called the “malicious and utterly false accusations” and said the company hoped to resume normal operations within a few days.

“I hope that those involved in fanning these flames will take a moment to contemplate what happened here today, and stop promoting these falsehoods right away,” Mr Alefantis said in the statement.