A construction crane collapsed on the new Port Mann Bridge Friday morning, dropping a 90-tonne concrete section of bridge decking into the water below.

Nobody was injured in the incident, said Max Logan, spokesman for the Port Mann-Highway 1 Improvement Project. He said the waterway below was closed to marine traffic due to ongoing work above.

At about 9 a.m. a gantry - a horizontal crane, or truss, used to install premade concrete deck sections - collapsed when its footings gave way.

An hour later, one of the blue legs of the crane atop the partly-built bridge appeared toppled, visible from the deck of the existing Port Mann.

While construction on the new bridge halted Friday, work continued on the roadway leading up to it. Heavy equipment worked the gravel road surface.

The approaches to the bridge span require about 1,000 concrete sections, Logan said, each weighing about 90 tonnes.

The fallen section will be salvaged from the river, he said. "At this point it's too early to say whether it's possible to use the piece."

Logan said the Port Mann Bridge project is a fixed contract and the dropped piece will not cost the province additional money.

Logan said the area was cleared after the incident and the contractor will investigate what went wrong. It's not known what caused the gantry's footing to buckle.

The dropped section was to form part of the 820-metre northern bridge approach on the shores of Coquitlam. Together with the 350-metre Surrey approach, they will make up just over half the completed bridge's two-kilometre length.

WorkSafeB.C. dispatched investigators to the site.