The Golden State Warriors' plan to build a waterfront arena in San Francisco is months behind its original schedule and the repair cost for piers to hold the venue has increased by as much as $50 million city documents show.

The team could miss its 2017 targeted opening and the new figure - if it holds - raises the question of who would cover the bill.

The basketball franchise's representatives dispute the cost projection and downplay the delays as routine for a complex project. They maintain that the arena will be ready for the start of the 2017-18 NBA season but acknowledge their schedule is tight - and doesn't leave much room for unforeseen problems.

"When we began this project we laid out a timeline that had a built-in cushion for the natural delays that occur on a project of this size" said Nathan Ballard a Warriors spokesman on the arena plan. "We've got a lot of work to do in a short time frame but we are confident we can complete it by 2017."

Mayor Ed Lee has called the arena "my legacy project." If successful it would bring an 18000-seat entertainment arena to the waterfront on Piers 30-32 just south of the Bay Bridge. The controversial proposal includes two parking garages a hotel and a condominium tower on a 2.3-acre parking lot just across the Embarcadero and more than 130000 square feet of retail space spread across both sites.

The initial $1 billion price tag is now even higher thanks to the escalating cost of rehabbing piers that have been a development graveyard.

At least five groups have given up on plans to build on Piers 30-32 since 1990 most recently billionaire Oracle co-founder Larry Ellison as part of the America's Cup regatta.