The metro line extension, the key legacy project of the Rio de Janeiro Olympics, will open just four days before the Games and offer only limited service.

State transportation secretary Rodrigo Vieira announced the plans in an interview on the broadcaster RJTV.

The delayed subway line is just one in a long list of problems confronting Brazil’s first Olympics, including the suspension last week on impeachment charges of the president, Dilma Rousseff. Other problems include the Zika virus, deep budget cuts, slow ticket sales and severe water pollution in the venues for sailing and rowing.

The subway extension will open on 1 August and links the Ipanema and Copacabana beach areas to the western suburb of Barra da Tijuca, site of the Olympic Park. The line will be available only to event ticket holders, athletes and media covering the games.

“Trains will be less frequent,” Vieira said. “This is compatible with just starting an operation, and also will meet the city’s demand with regard to the Olympics.”

The metro extension has repeatedly been delayed, partly because of funding shortfalls. The cost of the line is reported to have doubled from about 5bn Brazilian reals ($1.4bn) to about 9.7 billion reals ($2.8bn).

Two months ago Sidney Levy, the chief operating officer of the Rio Games, said the metro line would hold a “soft opening” a month before the games open on 5 August. Vieira said the line would be open to the general public after the Paralympics end in mid-September.

“The population that does not participate in the Games can use the subway the day after the Paralympics end,” Vieira said.

He said the subway would continue to operate on a reduced schedule after the Paralympics. “Over the months the operation will be refined,” Vieira said. “We will reduce the intervals between trains and will offer more capacity. When it is a mature operation, we will extend times and accommodate the 300,000 passengers per day, identified as the demand in the first year of operation.”