The deal would make Alcoa the world's largest aluminium firm

The proposed offer abruptly ends two years of merger talks between the two industry heavyweights.

A combined company would create the world's largest aluminium producer, Alcoa said.

Shares in Alcan closed up 34.08% at $90.57 in trading on the New York Stock Exchange. Shares in Alcoa also rose, up 8.33% to $38.63.

Strategic rationale

Alcoa's chairman and chief executive, Alain Belda, said he was "very disappointed" that two years of discussions to merge the businesses had been unsuccessful.

"We believe firmly in the compelling strategic rationale behind the combination of Alcoa and Alcan and are convinced that this transaction creates substantial value for both sets of shareholders and for our customers around the world," he said.

"We are therefore taking our offer directly to Alcan shareholders."

Mr Belda said the merger would create a "stronger, more diverse" global leader that would grow faster and be more competitive than the two companies on their own.

Increased financial resources would also allow a combined company to fund environmental projects, such as reducing greenhouse gas emissions.