Security scares across the U.S. prompted the evacuation of a terminal building at New York's LaGuardia Airport on Tuesday (April 16) and forced a plane at Boston's Logan Airport to undergo security checks on the tarmac, just one day after deadly bombings struck the Boston Marathon.

The U.S. Airways plane from Philadelphia landed at Logan Airport and was searched for a suspicious package while parked on the tarmac due to concerns over a piece of unclaimed luggage, officials said in a statement.

The bag was re-screened at the airport while the plane remained on the tarmac and was later cleared of any threat.

At New York's LaGuardia Airport, hundreds of passengers could be seen waiting on an overpass outside a terminal building and gathering outside entrances after a suspicious package prompted an evacuation.

The package was later identified by police as harmless and the terminal was reopened.

Port Authority spokesman Ron Marsico later said the suspicious package was "part of a light fixture" and that the airport had been given the "all clear".

Security has been heightened in busy cities across the United States following Monday's (April 15) double explosion which killed three people and wounded over 100 others at the finish line of the Boston Marathon.

Police presence has also been stepped up at landmarks and tourist areas across the country.

Presented by Adam Justice