Athletes and officials lavished praise on the Rio 2016 Olympic aquatics center after the opening day of its first official event on Friday.

Built at a cost of 38 million US dollars, the venue in the neighborhood of Barra da Tijuca has a capacity to seat 15,000 spectators.

"It's very beautiful. I'm impressed. It's a world-class swimming pool and fast," said Brandonn Almeida, who has achieved the Olympic qualifying standard for the 400m medley.

Friday was the first day of the five-day Maria Lenk trophy, which doubles as the final Olympic qualifying competition for Brazilian swimmers.

Minor construction work - such as a roof for an outside warmup pool and the installation of air conditioning - still needs to be completed.

But organizers are adamant the venue will be fully ready when the Olympics begin on August 5.

"We want to have the best possible conditions and the best possible competition, with lots of records, big crowds and a big (TV) audience," said Cornel Marculescu, the executive director of world swimming's governing body FINA.

"We are also realistic and there is a lot of work to do, but there is time," he added.