Fire gutted a luxury apartment complex under construction a few blocks from the Statehouse early Thursday, with flames consuming much of the six-story complex and gray smoke billowing across the downtown skyline. No injuries were reported.

The $28 million Cosmopolitan on the Canal complex was considered a total loss, Fire Department spokeswoman Rita Reith said. The cause of the fire, which broke out around 3:30 a.m., was not determined.

Jerry Collins, president of the developer, Flaherty & Collins Properties, said the complex was fully insured and he plans to rebuild.

The three interconnected buildings sat beside a pedestrian walkway-lined canal near several other residential and office buildings. Terri Dusenbery and her husband, who live nearby, briefly fled their condo out of fear the fire might spread.

"Our bedroom was bright orange and I thought, `What is going on?"' she said. "So I got up and looked out, and the fire was so intense our window was hot."

The project included 218 apartments, a parking garage, a canal-side cafe, a fitness center and 20,000 square feet of retail space, and the company had hoped to begin renting units in May.

About 125 firefighters brought the fire under control, Reith said. Authorities believed the fire, the biggest in 20 years in the city's downtown, began in the part of the complex abutting the canal, she said. A portion of that structure collapsed and firefighters were still pouring water on the smoldering building 13 hours after the fire broke out.

Collins said the portion of complex where the fire began was filled with construction supplies as workers had been finishing its interior and laying brick on its facade.

"There was a lot of wood in there, drywall and other construction supplies there," he said. "We were about three to four weeks away from charging up the sprinklers for the whole thing."

Reith said it may be days before investigators determine the cause of the fire, and that federal officials would assist because of the high financial loss in the blaze.

Mayor Greg Ballard said firefighters kept the flames from spreading to adjacent buildings. "It's a remarkable job how they got in there to do this," he said.

The upper floor of the nearby Historic Landmarks Foundation of Indiana headquarters sustained some damage, said Marsh Davis, the group's president. The building is a 1879 Italianate home that the organization restored and expanded in a $2.1 million project, according to the group's Web site.

Indiana Chief Justice Randall Shepard, honorary chairman of the foundation's board, said the building holds historical and architectural books that aid staff and volunteers in directing the restoration of historic buildings across the state.