A professional wrestler and actor has died after collapsing in the ring in front of fans during a bout in London, with witnesses criticising the amount of time it took for him to receive medical attention.

Silver King – who played a villain called Ramses in the film Nacho Libre alongside Jack Black and was a star in his native Mexico – was performing at the Roundhouse in Camden for an event titled “the Greatest Show of Lucha Libre”.

The wrestler, 51, whose real name is Cesar Barron, was believed to have died from cardiac arrest mid-performance, according to the organisers.

Following an exchange of moves with his opponent, Juventud Guerrera, also known as Youth Warrior, Barron collapsed on the canvas and did not get back up for about 30 seconds as the referee urged him to return to the choreographed wrestling match.

He eventually attempted to stand back up, at which point he was kicked by Guerrera and fell on to his front. Unaware of the nature of the incident, his opponent spent half a minute trying to turn him over before pinning him down and holding up his leg as the referee began slowly counting him out.

Video footage showed that the wrestler was lying still and apparently unconscious for about two and a half minutes before he was attended to, while Guerrera celebrated. However, none of the first responders appeared to be medical professionals and witnesses criticised the length of time it took before Barron was treated. It appeared from the video that no-one initially realised the severity of his condition.

“It was odd that no medics rushed up. It didn’t seem like anyone was on hand,” one witness told the Guardian. “Wrestlers then came out and started giving him CPR.

“The announcer said we will take a short break and dimmed the lights, but then a couple of minutes later told everyone to leave. Even as people were flooding out of the arena, there were no professional medical people on stage.”

Another witness, who was stood at ring side, said she also did not see anyone clearly designated as a medic in the ring. “People were asking ‘where are the first aiders’,” Carolina Gomez, a photographer at the event, said. “It was odd. A woman was giving him CPR while he still had his mask on, and then someone else did it. It was chaotic.

“They then started asking everyone to leave and we were ushered out as police and ambulances arrived. Everyone was stood in disbelief.”

The London ambulance service arrived soon after being called at about 10.20pm but were unable to resuscitate the wrestler and he was pronounced dead at the scene.

The Roundhouse said the circumstances of the wrestler’s death were being investigated. “Our thoughts and condolences are with his family, friends and all of the Lucha Libre team,” the venue said in a statement. Scotland Yard said police are treating his death as “non-suspicious”.

A Camden council spokesman said: “We will begin investigating the circumstances related to this incident from Monday.” It is understood that officers will examine health and safety matters, as well as licensing.

Lucha Libre World, the organisers of the show, said it was sorry to confirm the death of the former World Championship Wrestling star wrestler. “César Cuauhtémoc González Barrón (AKA Silver King) suffered what we believe was a cardiac arrest while performing in the show and sadly passed away.

“We have truly lost one of Lucha Libre’s greatest wrestlers and our thoughts and deepest condolences are with César’s family and his fans across the world. We will be able to make further announcements when more information becomes available.”

Tributes poured in from across the world for the stricken fighter. Jack Black posted an image taken during filming on Instagram with the caption: “Vaya con dios, hermano [go with god, brother]”.

The Canadian wrestler Chris Jericho thanked Barron on Instagram for teaching him to become a better fighter, while Mexican ‘Luchador’ El Hijo del Santo said he was “deeply saddened at the death of my great rival and companion at so many battles”, adding that Silver King “died as he wanted: fighting!”.

Lucha Libre wrestling involves competitors wearing elaborate costumes and colourful masks – which they must remove if they lose a fight. The show, which features aerial athletics, acrobatics and dramatic theatrics, is performed by freestyle wresters in choreographed battles.

Silver King competed in World Championship Wrestling between 1997 and 2000, taking on Juventud Guerrera for the cruiserweight championship in 1998. He grew up in a wrestling family in Torreón, northern Mexico, and his father was a popular lucha libre fighter named Dr Wagner.