An estimated 300 protesters demanding an end to Chinese rule in Tibet and to political repression throughout China lined the route Hu's horse-drawn procession took to Buckingham Palace, the London residence of Queen Elizabeth II.
Under heavy rains, many of the demonstrators waved banners and flags, including those of Tibet.
"Free Tibet" some of them shouted as mounted police and soldiers led the gilded carriage containing the president and the queen, who waved to the crowds.
Supporters of Hu and the Chinese government meanwhile waved their national flag.
Hu, who met Prime Minister Tony Blair in Beijing just two months ago, will spend two days in the British capital before going on to Germany and Spain, demonstrating a renaissance in Sino-European relations.
Mr Blair, who was among the welcoming party, said earlier that his formal talks with Hu would touch on trade, global security, climate change as well as "how economic and political developments are progressing in China".
Human rights
A Blair spokesman said human rights issues have been raised in the past and would likely come up again.
With Britain holding the rotating EU presidency, political analysts expect Hu to press hard for the lifting of a European arms embargo on China, imposed in 1989 after the snuffing of the Tiananmen Square democracy movement.
EU leaders initially pledged to remove the ban by June this year, but China's anti-secession law on Taiwan, passed in April, delayed that intention amid concerns of tension escalating across the Taiwan Straits
Present were activists for the Free Tibet Campaign, the Falungong religious movement, the Federation for a Democratic China (FDC), a group representing independent Taiwan and the Uyghur Association UK, which fights for the freedom of this Turkic ethnic group.
"We are determined to make sure he will see us and he will hear us," said Shu Li, head of the British branch of the FDC, some of whose activists took part in the protest.
"Hu wants to at least get the arms embargo to be lifted against China. We're lobbying the British and the European governments not to let him succeed because China's human record has not improved at all," Shu said.
"If anything it is getting worse." Shu said members of his federation would protest Hu's visit to Germany and Spain as well.
Mr Blair made it clear that, unlike a 1999 visit by Hu's predecessor Jiang Zemin, police would not block peaceful demonstrators from getting across their message to the Chinese leader.
Dalai Lama
Alison Reynolds, the director of the Free Tibet Campaign, alleged police used "heavy-handed" tactics in a bid to prevent activists from handing out small Tibetan flags to protesters.
She said earlier her group had written to all the British officials who would be meeting with Hu "urging them to press Hu Jintao to meet the Dalai Lama personally as the best means to resolve the occupation of Tibet".
During a visit to Washington for talks with US President George
W Bush, the Dalai Lama, the Tibetan spiritual leader who lives in exile in India, accused Beijing of imposing "very, very repressive" policies in Tibet.
Hu, who became China's head of state in 2003, was the top Chinese Communist Party official for Tibet when martial law was imposed in March 1999 after riots broke out in the region's capital Lhasa.
President Bush is looking forward to meeting the Dalai Lama, the White House said.
Speaking ahead of his meeting, the Dalai Lama claimed that China pursued strict rule in the Tibetan Autonomous Region despite "some progress" in direct talks between his envoys and Beijing to resolve the Tibetan question.
"Still, things are very, very repressive," the 70-year-old Tibetan leader told reporters.
The Dalai Lama will appeal to Mr Bush to urge Hu Jintao during their summit in Beijing later this month to give "genuine autonomy" to the Himalayan territory, said Lodi Gyaltsen Gyari, the Dalai Lama's special envoy.