Military police are facing off with protesters in the middle of Sao Paulo's metro system.

An ongoing strike by metro workers has tensions rising -- less than a week before the FIFA World Cup kicks off.

Friday's face-off saw police threaten protesters with guns.

A protester's hand can be seen trying to coax the police into lowering their weapons.

But like the ongoing worker negotiations, this attempt to calm the police proved futile.

The protest ended with tear gas, rubber bullets and stun grenades.

Of 63 stations throughout the city, 31 were closed.