BOSTON (AP) — The Massachusetts secretary of state has ordered all ballots in a congressional primary race sealed and locked away so they can't be tampered with in anticipation of a recount in the too-close-to-call election.

William Galvin says the two front-runners in the field of 10 candidates for the Democratic nomination in the 3rd Congressional District in northeastern and central Massachusetts were separated by just 51 votes Wednesday morning.

Lori Trahan, once chief of staff to former U.S. Rep. Marty Meehan, declared victory early Wednesday. But Daniel Koh, former chief of staff to Boston's mayor, has not conceded.

As of 9:19 a.m., Trahan had garnered about 200 more votes than Koh with 98 percent of precincts reporting, according to the latest Associated Press tally.

The candidates are vying to replace Democratic U.S. Rep. Niki Tsongas, who is not running for re-election.

This article has been updated.