LONDON, England (CNN) --
Police grab a protester as he tries to snatch the Olympic torch.
1 of 3 Hundreds of police officers were guarding the 31-mile route and flanking torch-bearers in an effort to prevent pro-Tibet campaigners from further disrupting the event. At least 25 people have been arrested, the Metropolitan Police said.
Crowds were lining the route across the city, with many waving Tibetan flags and "Free Tibet" banners.
Others carried signs reading: "Stop the killing in Tibet", "No Olympic torch in Tibet" and "China talk to Dalai Lama," the UK's Press Association reported.
Amid chaotic scenes, police officers grabbed a man in west London as he tried to snatch the torch from torchbearers.
Moments afterwards, a second man released a cloud of foam from a fire extinguisher as he tried to douse the flame. Watch as protesters almost extinguish the Olympic torch »
In a statement, the two men, Martin Wyness and Ashley Darby, said the relay was a propaganda campaign to cover China's "appalling human rights record," PA reported.
"Our protest is not directed at the Chinese people whatsoever but instead at the brutal Chinese regime that rules them," they said.
Three demonstrators were also arrested as they attempted to board a bus following the flame as Olympic gold medal-winning rower Steve Redgrave got the relay under way at Wembley Stadium, northwest London, The Associated Press reported.
The relay, which featured many sports stars and celebrities, was also halted as it passed through Oxford Street in central London when human rights campaigner Peter Tatchell jumped into the road carrying a sign calling for the release of Chinese activist Hu Jia, who was jailed on Thursday.
"The arrest last week of human rights activist Hu Jia shows that China is not fulfilling its human rights commitments which were part of the deal for them to get the Olympics," Tatchell told PA.
"At the very least, world leaders should boycott the opening ceremony and athletes should wear Tibetan flags when they go on the podium to receive their medals."
Police commander Jo Kaye said there had been a "small number of criminal attempts to disrupt the safety, security and safe passage of the torch."
"The Met has clearly stated in the build up to this event that we will facilitate lawful protest, however we will not tolerate continued attempts to breach the safety security and safe passage of the torch and its bearers. Our officers will continue to respond swiftly and appropriately to any further incidents."
Later, the relay appeared to pass without major disruption outside the Chinese embassy despite the noisy presence of large crowds of protesters.
Hundreds of pro-Beijing demonstrators were also gathered along the route and in Trafalgar Square with police separating them from anti-China protesters.
China's ambassador to the UK, Fu Ying, carried the torch through Chinatown, following a different route to originally planned, before handing it over without incident, AP said.
The rally also passed along Downing Street where UK Prime Minister Gordon Brown greeted the torch without holding it as it was carried by former British Olympic athlete Denise Lewis.
Brown has resisted calls for a sporting boycott of the Summer Games. London is due to host the next edition of the Games in 2012.
"It is also important to recognize, when you ask the question about the Olympic torch, that the Dalai Lama himself has said that he does not want to see a boycott of the Olympics," Brown said Saturday.
The torch's epic passage from Greece to Beijing has become a target for human rights campaigners opposed to China's hosting the Games, with further protests expected as the flame passes through cities including Paris, San Francisco and New Delhi before reaching the Chinese mainland next month.