A team of U.S. Capitol Police (search) carrying automatic weapons guarded a harborfront hotel and work crews dropped metal barriers around City Hall as security forces on Sunday completed preparations for the Democratic National Convention (search).

"These next few hours certainly will be important as different units and agencies are settling into their roles," Massachusetts State Police Sgt. David Paine said. "But it's nothing new to these people. They're ready."

Camouflaged military police staked out elevated subway lines overlooking the FleetCenter (search), where 4,350 delegates will convene Monday through Thursday to nominate their presidential candidate. A surveillance helicopter often hovered over the area.

Bomb-sniffing dogs and officers roamed nearby streets. Metal barricades about 7 feet high directed foot traffic. In other ways, however, Boston was eerily quiet for a sunny summer day that would normally be bustling with tourists.

The Capitol Police were providing security for those staying at the Boston Harbor Hotel, but officials would not disclose details. The U.S. Coast Guard patrolled the harbor and expected to board commercial ships at random for security checks.

State officials prepared to shut down Interstate 93, a major highway that runs just feet away from the arena. Officials began erecting temporary curbing on I-93 north of the city Sunday morning, setting up special routes for emergency crews and buses. During the convention, a 6-mile stretch of highway will be shut down from 4 p.m. to 1 a.m.

"It is a massive undertaking and we're trying to do it way that has the least impact on commuters," said Mariellen Burns, spokeswoman for the group coordinating security and transportation for the event. "But there's definitely going to be inconveniences. We know that."

The Federal Aviation Administration banned all corporate and private flights in and out of Logan International Airport during the convention. Only regularly scheduled commercial flights, law enforcement, military and emergency medical flights will be allowed within a 10-mile radius of the airport.