FILE - In this Tuesday, July 16, 2013, file photo, an Amtrak conductor checks the time as the passenger train takes on passengers in Hanford, Calif. California's high-speed rail project reaches a milestone Tuesday, Jan. 6, 2015, as officials mark the start of work on the nation's first bullet train, which is designed to whisk travelers at 200 mph between Los Angeles and San Francisco in less than three hours. (AP Photo/Rich Pedroncelli, File)

FRESNO, Calif. - California's high-speed rail project reaches a milestone Tuesday as officials mark the start of work on the first U.S. bullet train, which is designed to whisk travellers at 200 mph (320 kph) between Los Angeles and San Francisco in less than three hours.

The ceremony in Fresno comes amid challenges from Central Valley farmers and communities in the train's path who have sued to block it and from Republican members of Congress who vow to cut funding for the $68 billion project. Opponents also say the state can't deliver the sleek project as it was first promised.

Dan Richard, chairman of the California High-Speed Rail Authority, acknowledges the authority has been slow to buy up most of the land needed for laying track, but he is confident the system will be built, making California a model for high-speed rail across the country.

"The voters are going to get exactly what they asked for," Richard said. "We have never ever stepped away from that vision, not one inch."

Californians in 2008 approved a nearly $10 billion bond for the train, and in 2012 the Obama administration dedicated $3.3 billion in stimulus funds. The state Legislature last year dedicated to the project a portion of the greenhouse gas fees collected under the state's cap-and-trade program to reduce greenhouse gases.

Gov. Jerry Brown, a staunch advocate of the train, is expected to attend the groundbreaking along with hundreds of other dignitaries.

Bullet train systems in other countries generate revenue, and California officials are banking on this one to entice private investment as well as to generate revenue from advertising and development around the stations.

To make way for tracks, some demolition started last year in Fresno, but officials say work this year will be more intensive along the project's first segment — a 28-mile (45-kilometre) stretch from Fresno north to Madera. A second phase of work will occur along the 114 miles (183 kilometres)from Fresno south to Bakersfield. Plans call for completing first 520 miles (837 kilometres) linking San Francisco and the Los Angeles Basin by 2029.

Rep. Jeff Denham, a Central Valley Republican and outspoken critic of high-speed rail, vows to block any federal money for the trains because he doesn't believe they'll be as fast or carry as many riders as initially promised. Without funding, he said, the project won't move beyond an initial stretch in the Central Valley.

"It's hard to celebrate breaking ground on what is likely to become abandoned pieces of track that never connect to a useable segment," Denham said.

Officials say design and planning already has created 632 jobs, and that the workforce will rise to 20,000 over the next five years.

Fresno Mayor Ashley Swearengin, a Republican, said she backs the rail system. In addition to putting construction workers on the job in the short term, Swearengin said the rail project will connect the Central Valley agricultural region with other sectors of the state's economy. "We're stuck right in the middle and it's difficult to get in and out," she said. "It fills a deficit for Central California."

News from © The Associated Press, 2015