A star-studded benefit concert for victims of the Manchester bombing kicked off to tearful fans, heavy police guard and clattering helicopters on Sunday, just a day after another militant attack in London.

Emotions ran high as fans - many with colorful face make-up, costume bunny ears and the popular Manchester Bee t-shirts - poured into the city's Old Trafford cricket ground for the show headlined by pop star Ariana Grande, whose May 22 concert ended with 22 dead and over 100 wounded when a bomber struck.

Some broke down in tears, while others clapped, danced and joked with police officers on horseback patrolling the crowds. The event began with a moment of silence for the victims of the bombing less than two weeks ago.

"I don’t want to feel or hear or see any fear in this building," singer Pharrell Williams told the crowd as he led them in a rendition of his hit single "Happy." "The only thing we’ll feel here tonight is love, and positivity."

Fellow singer Miley Cyrus joined the rendition and said: "I’d like to wrap my arms around each and every one of you and thank you ... The most important responsibility we have in this time is to take care of one another."

Those who attended Grande's May 22 concert were given free tickets to attend Sunday's concert, with some persuaded to attend by their affection for the pop star.

"I’m real excited, but real scared," Shannon Beetham, 14, who was injured in last month's bombing, told Reuters. "We were there in Manchester (arena) as well, I was hit."

Scores of police backed up by armed officers watched over the crowd. Helicopters circled overhead and officers on horseback made their way through the crowds. Attendees were patted down and sniffer dogs patrolled the grounds.

Police had warned concert-goers of additional checks after Saturday's attacks in London that left seven dead when a van plowed into pedestrians and three attackers stabbed people.

Laura Simpson and her daughter Milly, 10, told Reuters they also had doubts about attending the concert, after Milly narrowly avoided being involved in the attack last month.

"She left 5 minutes early because she was tired," Laura said of her daughter, who was dressed in an Ariana Grande t-shirt. "We weren't sure about coming today, were we? Everyone's just a little bit on edge."

The event opened with a moment of silence for the victims of the bombing, followed by poet Tony Walsh reading his poem "This is the Place" - which drew wide attention in the days after the attack.

In addition to Grande, Sunday's concert was due to feature performances from acts including Coldplay, the Black Eyed Peas, Justin Bieber, Take That, Katy Perry and Usher.

The concert was being broadcast in Britain by the BBC, which said networks in 38 other countries would also broadcast the show.