RIO DE JANEIRO (REUTERS) - Sixteen people have been hit, and four killed, by stray bullets so far in January in Rio de Janeiro, according to the police, intensifying security concerns ahead of the 2016 Olympic Games.

On Monday a 58-year-old woman was hit in the head while asleep in her home and a 12-year-old child was shot in the leg: both survived.

On Sunday, a 21-year-old woman died after being hit in the liver.

Authorities attribute the stray gunfire to drug traffickers.

The number of victims is seen by some as evidence of escalating violence in Brazil's postcard city, which has long struggled with heavily armed drug gangs operating in the favelas, or slums, dotting the surrounding hillsides.

Local government and Olympic organisers insist that athletes and tourists will be safe when they come for the Games in 2016.

In recent years, Rio has invested heavily to enlarge the police force, particularly in the favelas that for decades were largely beyond the rule of law.

Critics argue that flooding the favelas with police is not sustainable and that the original success has worn off.

The money to support such a security push is also no longer as readily available, as Brazil introduces austerity measures in an attempt to shore up its finances and avoid a credit rating downgrade.

The 2015 budget for the military police in the state of Rio de Janeiro has been cut by 26 per cent, Brazilian daily O Globo reported on Tuesday.