UPDATE 4-Hong Kong has 'risen from the ashes', China's Xi says on rare visit

* China's Xi arrives in Hong Kong via high-speed rail

* Will swear in city's new leader and mark anniversary

* Britain and U.S. say China failed to meet commitments

* Police warn against violence, disorder

* Tight security around train station (Adds U.S. and British criticism of China)

By Marius Zaharia

HONG KONG, June 30 (Reuters) - Hong Kong has overcome its challenges and "risen from the ashes", China's President Xi Jinping said on Thursday, as he arrived in the former British colony to celebrate 25 years since its return to Chinese rule.

After Xi began his first visit to the city since 2017, British Prime Minister Boris Johnson and U.S. Secretary of State Antony Blinken said China had failed meet its commitment to respect a "One Country, Two Systems" arrangement agreed under the deal that ended British colonial rule in 1997.

Johnson said Britain would do all it could to hold Beijing to its commitments, while Blinken said: "We stand in solidarity with people in Hong Kong and reinforce their calls for their promised freedoms to be reinstated."

On Friday, Xi will swear in the global financial hub's new leader, John Lee, on what is his first known trip outside the mainland in more than two years, amid the COVID-19 pandemic.

Wearing masks, Xi and his wife, Peng Liyuan, stepped off a high-speed train to be greeted by children waving flowers and Chinese and Hong Kong flags and chanting "Welcome, welcome, warmly welcome" in Mandarin.

"Hong Kong has withstood severe tests again and again, overcoming challenges one by one," Xi said in a brief speech. "After the wind and rain, Hong Kong has risen from the ashes."

Authorities organised a lion dance celebration while a police band played. Security was tight at the train station with police making stop-and-search checks, assisted by sniffer dogs.

Some analysts see Xi's visit as a victory tour after Beijing tightened its control of Hong Kong with a sweeping national security law, following mass pro-democracy protests in 2019.

"It is a celebration of the central government's victory over the political opposition in Hong Kong," said John Burns, a professor in the Department of Politics and Public Administration at the University of Hong Kong.

Outgoing city leader Carrie Lam and her husband were among those who welcomed Xi at the station, which has not been used for two years because of COVID restrictions.

Streets were festooned with red China flags and posters declaring a "new era" of stability.

Xi's full official schedule for the visit has not been released. It was not immediately clear if the celebrations would be affected by an expected typhoon.

On his last visit to Hong Kong, Xi warned against any acts endangering China's sovereignty, saying the city needed to beef up its national security arrangements.

Tens of thousands of demonstrators marched during Xi's visit five years ago, but no protests are expected this time because of the city's heightened security and with the most outspoken opposition politicians and democracy activists either in jail or self-exile.

Beijing and Hong Kong's government say they have "restored order from chaos" so that the city can prosper.

In a statement, Blinken said the 25th anniversary of the handover was envisioned as the halfway point of 50 years of promised autonomy under "One Country, Two Systems".

"Yet it is now evident that Hong Kong and Beijing authorities no longer view democratic participation, fundamental freedoms, and an independent media as part of this vision," he said.

"Authorities have jailed the opposition ... raided independent media organizations ... weakened democratic institutions, delayed elections," Blinken said. "They have done all of this in an effort to deprive Hong Kongers of what they have been promised."

WARNINGS AND COVID TESTS

Lui Kam-ho, a senior policeman, warned this week against any acts of violence or public disorder. The police force of more than 30,000 said it would ensure security for the celebrations.

Police closed parts of Hong Kong, blocking roads and enforcing a no-fly zone over Victoria Harbour.

Resident Karis Ho, 31, said the security measures were an inconvenience for the public and "made Xi appear sensitive".

Angel Chau, 62, was excited.

"It shows how much he values Hong Kong," Chau said.

Members of the pro-democracy League of Social Democrats said they would scrap plans for demonstrations after national security officers warned them not to protest during Xi's visit.

Incoming leader Lee, a former policeman Washington has placed under sanctions over the national security law, and Lam have been taking daily COVID tests and staying in a quarantine hotel for days before Xi's visit, media said.

Hong Kong reported 2,358 COVID cases on Thursday, with daily infections rising.

China's strategy of stamping out COVID outbreaks as soon as they occur, at just about any cost, contrasts with a global trend of co-existing with the disease.

Some journalists have been blocked from covering the ceremonies, with authorities citing security requirements.

Xi, poised to secure a precedent-breaking third leadership term at a Communist Party congress this year, was expected to spend the night in the neighbouring city of Shenzhen on Thursday before leaving Hong Kong on Friday. (Reporting by Hong Kong and Beijing bureaus and David Brunnstrom on Washington; Writing by Marius Zaharia and David Brunnstrom; Editing by Clarence Fernandez, Robert Birsel and Richard Pullin)