FRESNO, California (AP) -- 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 travelers 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-kilometer) stretch from Fresno north to Madera. A second phase of work will occur along the 114 miles (183 kilometers) from Fresno south to Bakersfield. Plans call for completing first 520 miles (837 kilometers) linking San Francisco and the Los Angeles Basin by 2029.