MONTREAL -- The federal government is coming under attack for its handling of one of Canada's busiest bridges.

NDP Leader Thomas Mulcair says Prime Minister Stephen Harper needs to personally take charge of plans to build a replacement for Montreal's crumbling Champlain Bridge.

Mulcair says the Conservative government's handling of the file has been "inexcusable" and says construction of a new bridge should have been in place a long time ago.

The Champlain Bridge is one of several bridges falling under federal jurisdiction.

The deterioration of a supporting beam this week has led to major repair work and lane closures.

The bridge was built in 1962 and plans are underway to replace it with a new structure in 2021.

Federal Transport Minister Denis Lebel said Friday that the government is looking at speeding up construction of the new bridge on the St. Lawrence River.

The cost is pegged at between $3 billion and $5 billion.

More than 50 million vehicles use the Champlain Bridge every year. It links Montreal with its south shore suburbs.