The rest of the system experienced a much bigger problem, an underfrequency, since the system had a lot of load and not enough generation capacity. Some generators tripped because of the overfrequency, which aggravated the problem, and after an automatic rejection of 35% of the sub-system load the underfrequency did not go away. This caused the system to break in many pieces, São Paulo and Rio de Janeiro states were split with a few areas remaining online. Most of the Minas Gerais system remained online, and powered Brazil's capital, Brasília, as well as the state of Goias and some of Espirito Santo. In Rio, the military police placed 1,200 men in the streets to avoid looting. In São Paulo, traffic authorities announced they closed the city's tunnels to prevent robberies. More than 60,000 people were on Rio's subway when lights went out.