A major airport in northern Japan reopened Wednesday after bomb squads barricaded the area around an unexploded bomb from World War II.

Flights resumed at Sendai Airport after military troops worked through the night to pile sandbags around the 250-kilogram (550-pound) bomb, which was uncovered during construction near a runway two days earlier.

The airport, a regional hub for northeastern Japan, was closed all day Tuesday, with 92 flights cancelled.

The rust-covered bomb was surrounded by sandbags and the area around it sealed off so that flights could start up again. Officials said that although it was not clear what condition its detonator was in, the fear that it would go off by accident was low.

Sendai Airport was closed for months due to severe damage from last year's tsunami. The bomb was uncovered in construction related to its restoration. Officials said it could take a week to actually dispose of the bomb, which would have to be transported elsewhere or readied for a controlled detonation on site.

The United States heavily bombed Japanese cities during World War II, and finding unexploded bombs is not unusual, even 67 years after Japan's surrender. Dozens of duds are uncovered in Tokyo each year, and even more are found on the southern island of Okinawa, which was the site of the most intense fighting during the war.

Many of them are found at construction sites. The rusty condition of the bombs can make them prone to detonate when moved, but injuries are rare. Experts say it could take several decades to remove all of the unexploded ordnance.

Last week, hundreds of residents in central Tokyo were evacuated so that bomb squads could remove a 220-kilogram dud buried there.