Tension is growing in Ferguson, Missouri, in the runup to the announcement of a grand jury decision over whether to charge the officer responsible for the shooting of unarmed black man Michael Brown, 18.

Storefronts are being boarded up and residents are preparing for the worst, while the authorities, including Missouri Governor Jay Nixon, say the National Guard will be ready to step in if necessary.

Gun sales have increased by 300 percent, according to CNN, which interviewed a local business owner who said that customers bought 100 guns every weekend last month, while a typical weekend brings in about 30 buyers.