Hundreds of demonstrators gathered Thursday night in downtown Beirut in fresh protests against Lebanon's ruling elite and a months-long garbage crisis that activists warn has become a menace to public health.

The crisis began in July when the closure of a landfill caused rubbish to pile up on Beirut's roadsides, in parking lots and river beds.

There are fears the uncollected waste, coupled with the looming rainy season, could spread diseases such as cholera among the population.

"This isn't a political issue, this is a sanitation issue that affects the whole country," one protester told AFP.

In a message aimed at those Lebanese who had not joined the long-running "You Stink" protest movement, he asked: "Aren't you afraid that your children will get sick?"

Thursday's protest began peacefully but security forces fired tear gas and water cannons after some demonstrators attempted to remove safety barriers and block a road in central Beirut, an AFP photographer said.

The Lebanese Red Cross said 35 people were treated for breathing problems at the scene.

Under public pressure, the government approved in September a plan to tackle the rubbish crisis, but campaigners said it was too vague and did not meet their demands.

Beirut municipality on Wednesday announced a raft of precautions to prevent the spread of diseases.

Lebanon's last legislative elections were held in 2009, and parliament has twice extended its own mandate, citing internal political divisions and regional instability as justification.