LONDON – Demonstrators grabbed at the Olympic torch, blocked its path and tried to snuff out its flame Sunday in raucous protests of China’s human rights record that forced a string of last-second changes to a chaotic relay through London.

The biggest protests since last month’s torch-lighting in Greece tarnished China’s hope for a harmonious prelude to a Summer Games celebrating its rise as a global power. Instead, the flame’s 85,000-mile journey from Greece to Beijing has become a stage for activists decrying China’s recent crackdown on Tibetans and support for Sudan despite civilian deaths in Darfur.

Demonstrators attempted to board the bus trailing the torch shortly after British five-time gold medal rower Steve Redgrave started the relay at Wembley Stadium.

Less than an hour later, a protester slipped through a tight police cordon and gripped the torch before he was thrown to the ground and arrested.

“Before I knew what was happening this guy had lurched toward me and was grabbing the torch out of my hand and I was determinedly clinging on,” former children’s television host Konnie Huq told British Broadcasting Corp. television.

“I do feel for the cause,” she said. “I think that China have got a despicable human rights record.”

Another demonstrator tried to snuff the flame with a spray of white powder from a fire extinguisher, police said. Still others threw themselves in the torch’s path. They were tackled or dragged off by police. Authorities said 37 people were arrested.

London’s Metropolitan police said some 2,000 officers, on foot, motorcycles, bikes, and on horseback tried to keep the procession under control.

The demonstration swelled near where Chinese Ambassador Fu Ying was expected to carry the torch. Frantic organizers shuffled the order of participants and Fu unexpectedly appeared in the heart of Chinatown, jogging unhindered with the torch before handing it to the next runner.

But there were ugly scenes between Trafalgar Square and Big Ben, where a dozen protesters charged the torch.

“Everyone was running at (me). It was a bit weird,” said Scott Earley Jr., 17, the torchbearer.

About 100 demonstrators managed to impede the flame’s progress by surrounding it near St. Paul’s Cathedral, forcing police to put the flame on a bus.

“They’ve called the torch relay a journey of harmony, but on the ground in Tibet they are shooting and killing peaceful Tibetan protesters,” said Matt Whitticase, spokesman for the London-based Free Tibet Campaign.

Associated Press writers Regan McTarsney, Marcus Wohlsen and Angela Doland contributed to this report.