Authorities in London are doing their best to rule out the slightest danger of anything going wrong during the G20 summit. And on the other side, protesters are getting ready to make their point, too.

World leaders have come to London. And so have thousands of anti-capitalist, environmental and other demonstrators. London police are facing what they call an "unprecedented security challenge."

The Bank underground station was temporarily closed on Tuesday, and roads cordoned off after a suspect package was found.

Prime Minister Gordon Brown assures that police will act quickly if there's any threat to property or people.

Authorities have advised workers in the financial district to wear casual clothing, or consider working at home to avoid demonstrators' ire, though many say they feel everything will be fine.

Thousands of officers will be on duty, some armed with stun guns. Patrol boats and divers will ply the River Thames.

But protesters say police are exaggerating the potential for violence.

Camilla Power, Protester, said, "It's like a popular festival, it's April Fools Day, financial fools day. The people are coming to laugh the bankers out of town."

Police say the majority of protesters will be peaceful. But they're concerned about the actions of small groups. They fear some small groups might break from peaceful marches into violence.

(CCTV April 1, 2009)