(Adds Clyburn, Periscope quotes)

By Amy Tennery

June 22 (Reuters) - Democrats demanding action on gun control turned to Twitter's Periscope and Facebook's live video platform to broadcast their "sit-in" on the floor of the U.S. House of Representatives on Wednesday after the chamber's cameras shut down.

Representative Scott Peters of California told Reuters he downloaded the online video platform Periscope from the House floor after it became clear that chamber cameras were not operating.

"Thanks to them, the American people got to look in on and listen to what is taking place this floor," U.S. Representative James Clyburn of South Carolina said in praise of the platform.

The protest was the latest move by Democrats to persuade the Republican majority in Congress to take up votes on gun control measures in response to last week's mass shooting in Orlando, Florida, the deadliest in modern U.S. history.

"The speaker (Paul Ryan) controls the cameras," Peters said. "We noticed that over lunch, he turned them off - allowed them to be turned off."

A spokesman for Twitter said that tweets from Peters' account containing the Periscope footage had been viewed over 800,000 times as of Wednesday night.

Ryan's spokesman, AshLee Strong, said in a statement: "The House cannot operate without members following the rules of the institution, so the House has recessed subject to the call of the chair."

At about noon EDT (1600 GMT), presiding House officer and Republican Representative Ted Poe declared the House not in order, as Democratic protesters sat at the front of the chamber.

Cable news channel C-SPAN, which typically uses the House cameras to broadcast live footage of Congress, broadcast Peters' Periscope and other lawmakers' feeds.

Other news networks and cable news channels, including MSNBC, FOX and CNN, also ran parts of the footage.

C-SPAN communications director Howard Mortman said it was the first time the channel broadcast a live social media feed from the House floor.

"The House controls the cameras and that means they control the camera angles, the audio, video, the whole thing," Mortman said. "We're using social media platforms to show what's happening."

"With official broadcasts suspended in the House, we've created a channel to follow #NoBillNoBreak on #Periscope live," Periscope said in a tweet.

Peters said about five or six Democratic House members had broadcast live video during the sit-in. Late Wednesday, lawmakers cheered their thanks during one of his feeds that aired on C-SPAN.

One representative, Eric Swalwell of California, published live video from the House floor to Facebook.