Aluminium Bahrain, the world's fourth-largest producer, is in full operation, it said on Tuesday, despite weeks of protests and the government's declaration of martial law.

"Aluminium Bahrain is operating at full capacity, and remains unaffected by the current situation in the kingdom," the company said in a statement.

"The company hasn't suffered from any logistical disruption in the supply of raw material nor in the production and the export of aluminium."

Alba, which produces around 860,000 tonnes of aluminium per year, said it have put in place contingency plans "for any eventuality if and when the need arises".

"The only contingency measures taken by Alba up until now was the adjustment of the organization's workforce shifts," it said, without giving further details.

Bahrain declared martial law on Tuesday, looking to end weeks of protests by its Shi'ite Muslim majority, with Saudi troops on hand in the Sunni-ruled kingdom to help quell the unrest.

The growing unrest has led to staff shortages at the island's ports and slower operations although terminals remained open, shipping sources said on Tuesday.