Police have arrested nine people and issued dozens of dispersal orders after shoppers were locked inside stores on London’s Oxford Street following warnings of a robbery campaign organised on social media.

Hundreds of teenagers gathered outside JD Sports on the capital’s busiest shopping street in an apparent response to widely shared posts on Snapchat and TikTok urging users to take part in an “Oxford Circus JD robbery” at 3pm.

Just after 3pm, two young men were seized by police who were guarding the area in anticipation of trouble. Both men were detained outside a McDonald’s, three doors east of JD Sports. One of the young men, wearing a green hoodie, was detained by four officers. The other in a grey tracksuit was held by three officers.

The incident prompted twitchy security guards at a number of nearby stores, who were on alert for a possible shoplifting spree, to lock their customers inside their stores for several minutes. They included Muji, an opticians, and Boots, which lowered its storefront metal shutters.

Four police officers on horseback briefly struggled to maintain order as onlookers crowded the scene to video the incident on their phones. Traffic on Oxford Street was temporarily held up, as private security personnel urged the crowds to move on.

Minutes later police chased another group of young men suspected of shoplifting, prompting another surge in young people keen to capture the scene on their phones. One man was searched by three officers as he lay on the pavement.

Puzzled older shoppers asked police officers what was going on. They were told it was a police operation to stop shoplifters. An officer was overheard saying the young men were released without charge after being searched.

Just after 8pm, the Metropolitan police said it issued 34 dispersal orders and arrested nine people. A statement read: “Four people were arrested on suspicion of breaching the dispersal order, one person was arrested on suspicion of going equipped to steal, one person arrested on suspicion of assaulting a police officer, and one person was arrested on suspicion of a public order offence.

“Earlier in the afternoon, officers arrested two people in Essex for conspiracy to commit robbery following online social media posts.”

Earlier, the London mayor, Sadiq Khan, urged people not to take part. He said: “I am worried about this nonsense we have seen on TikTok encouraging people to go to Oxford Street.”

I’d encourage anybody who’s seen it not to go to Oxford Street. Do not allow yourself to be sucked into an area that could be a high-crime area.”

Police in Westminster had warned there would be heavy police presence in the area. In a Twitter post they said: “We are aware of online speculation about opportunities to commit crime around Oxford Street. There will be a significant number of our officers in the area over the next 24 hours.”

Some of those who had gathered said they were there out of curiosity. Harry, 14, from Islington, said: “I’m not here to steal anything, I’ve been raised better than that.”

Pointing to his phone he added: “I just want to record it.” He said he had heard about the event on Snapchat.

CJ, 16, from Cheshunt, Hertfordshire, said: “We’re not here to steal stuff – there’s loads of famous people making videos. We just saw loads of police and want to see what it’s about.”

Before 3pm some of the boys who gathered outside JD Sports were questioned by the police about why they were there. They gave vague answers.