Rio de Janeiro, Jul 31 (IANS): A part of a velodrome built for the 2016 Rio Olympics here was destroyed in a massive fire, Brazilian authorities said.

Located in the Barra de Tijuca district, the velodrome's construction was reported as one of the costliest projects undertaken by the city, reports Efe news.

The fire at the cycling track began at about 1 a.m. on Sunday, just six days away from the one-year anniversary of the Rio Olympics' inaugural ceremony, and authorities attributed it to a paper balloon with a burner inside that landed on its roof, although such objects are prohibited in Brazil.

Sports Minister Leonardo Picciani lamented the tragedy in a communique but refrained from discussing the roof damage, and it was unknown whether the track, the seating or the building itself were damaged.

He said that authorities would await the results of the investigation to determine the actual cause of the fire, and they will evaluate the damage and the measures to be taken to repair "this important national property".

The velodrome, one of the structures comprising the Olympic Park and said to have one of the fastest cycling tracks in the world, was used for cycling competitions during the Olympics last August but since then it has remained practically unused.

The cycling track cost 143 million reais ($45 million), was inaugurated in June 2016, six months behind schedule, and was the last Olympic project to be completed.

Despite the lack of use the venue has had since the Olympics, it costs about 11 million reais per year to maintain, since its special and delicate track requires constant use of air conditioning.