The city of Rio de Janeiro will offer more than 500,000 free tickets for this year's Olympic and Paralympic Games to children and public servants, officials said on Monday.

Rio's city government said it spent 52 million reais (14 million US dollars) on the initiative, designed to reward high performing students, adults who work with people with disabilities and public sector workers who contribute to promoting the Games on social media.

"Our aim is not only to improve the experience of our population in relation to the Paralympics, but also to help with the sale of tickets," said the mayor's office secretary Pedro Paulo.

Less than a third of the 2.5 million tickets available for the Paralympic Games - which run from September 7 to 18 - have been sold.

Meanwhile some 3.5 million tickets for the Olympics, to be held from August 5 to 21, have been purchased out of 5.7 million put on sale so far.

For Rio's public servants there will be 64,524 pairs of tickets available for the Paralympics and 4,000 pairs for the Olympics.

To secure the tickets, workers have until June 13 to submit photos and videos that can be used to promote the Games on social media. Applications can be made by accessing the Rio government's ingressocarioca website.

Another 177,000 pairs of Paralympic tickets are being offered to public school children, who will also be allocated 19,000 pairs of Olympic tickets.

The tickets will be distributed to students from first to ninth grade who secure top marks in the first half of the year.

In addition, the government is giving away 8,500 pairs of Paralympic tickets and 500 pairs of Olympic tickets for those who work with people with disabilities.

The announcement came as officials outlined measures taken to improve accessibility for people with disabilities to the city's public transport system.

Rio's transport secretary, Rafael Picciani, said the first phase of a new light rail service linking the city centre to the revitalized port district will begin operating on June 5.

He said that all Olympic transport projects - which also include a new subway line and bus routes, will be accessible to people with special needs.