As a group of dozens of athletes and celebrities makes its way along the 31-mile relay route through London's streets, protesters have been continually jumping through the police cordon, and one activist tried to seize the torch.
The protests have focused on China's clampdown the Tibetan independence movement.
Two activists were arrested after attempting to put the torch out with fire extinguishers. The men subsequently issued a statement to the press saying: "Our protest is not directed at the Chinese people whatsoever but instead at the brutal Chinese regime that rules them."
The international torch relay is an "elaborate propaganda tool" to cover up rights abuses in China, the statement said.
The relay, which began at Wembley Stadium, is set to last over seven hours. The relay team will travel on foot, bus, and boat, taking a circuitous route that crosses Leicester Square and London Bridge in the city center, and will end up at the O2 stadium in north Greenwich.
Around $2 million has been spent on security for the event.
Since a Chinese crackdown on mass protests in Tibetan capital Lhasa in mid-March, international attention has been focused on human rights in China, and several European Union countries have called for a boycott of the August 8-24 Olympic Games.
The protests in Tibet began on March 10, when Buddhist monks held a demonstration marking the 49th anniversary of a failed uprising against Chinese rule of the mountainous province. The rallies turned violent four days later, when exiled Tibetans say Chinese forces launched a brutal campaign of arrests and shooting, killing around 140 people. Beijing says only 13 people were killed, 12 of them Han Chinese murdered by Tibetan separatists.
