G20 in Pittsburgh

Police move to arrest a protester blocking a vehicle in the roadway in Pittsburgh, Pa., on Thursday, Sept. 24, during the first day of the G20 summit. Global leaders began arriving last night and will continue to arrive all day prior to the official welcome ceremony this evening.

U.S. President Barack Obama and first lady Michelle Obama arrive Thursday at the Phipps Conservatory in Pittsburgh for an opening reception and working dinner for heads of delegations.

Members of the International Burmese Monks organization march past police officers during a demonstration near the David L. Lawrence Convention Center in Pittsburgh on Thursday.

A woman holding a child makes a V-sign as protestors march through the Lawrenceville section of Pittsburgh on Thursday.

Demonstrators walk away from pepper gas released by police during a protest prior to the start of the G20 summit on Thursday.

A demonstrator sprays water over the face of another demonstrator after police released pepper spray during a protest Thursday.

A man holds an American flag upside down near a military checkpoint in downtown Pittsburgh on Thursday.

A National Guardsmen and local residents pass by a welcome mural near the site of the G20 Summit on Thursday. Military forces from Pennsylvania and police from various states were called in to secure the city for the event.

Chinese people carry a banner that reads 'We Warmly Welcome' Chinese President Hu Jintao upon his arrival at the Pittsburgh International Airport for the G20 Summit on Thursday. Leaders from the world's 19 largest national economies and the European Union are gathering for the two-day G20 Summit and will discuss international trade, energy and climate change among other issues.

US Secret Service divers work in the Allegheny River along the edge of the David L. Lawrence Convention Center in Pittsburgh on Thursday.

Riot police block a street during anti-G20 protests in Pittsburgh on Thursday.