Spain's central government says the planned referendum violates Spain's constitution, and the Constitutional Court has ordered it suspended while it studies its legality. Each of the ferries has a capacity of over 6,500 passengers.
Acting on a judge's orders, police seized 10 million ballot papers and arrested at least 12 people, mostly Catalan government officials, suspected of coordinating the referendum.
Nicola Sturgeon has criticised Spain for its attempts to block a Catalan independence vote as members of her party's youth wing prepare to travel to Barcelona in support of the breakaway movement.
The ministry did not say how many extra federal police are being sent but local media put the figure at 3,000 to 4,000.
They will join the approximately 5,000 state police normally based in Catalonia and around 17,000 Mossos officers.
An Interior Ministry statement said the extra agents would provide backing for the Catalan regional police, who are also under orders to prevent the staging of the referendum.
OECD revises up Japan's 2018 growth forecast to 1.2 percent
However, the recovery of business investment and trade remain too low to sustain healthy productivity growth, the OECD said. Globally, the pace of expansion is expected to pick up this year compared to 2016, with a further uptick projected in 2018.
There were reports that people wave "Esteladas" (pro-independence Catalan flags) during a pro-independence demonstration, on September 11, 2017 in Barcelona during the National Day of Catalonia, the "Diada". The national interior ministry's press office didn't respond to multiple requests for comment.
Hundreds of pro-independence supporters had protested outside the courthouse in the town of Hospitalet de Llobregat to demand the officials' release. The Constitutional Court ruled that Catalonia lacks the unilateral right to self-determination because fundamental matters such as changing the country's borders can only be decided at a national level.
Catalonia represents a fifth of Spain's 1.1-trillion-euro ($1.32 trillion) economy and enjoys wide self-government.
Bigio warned that the incarceration by the central government of regional officials and protesters in Catalonia will inflame the tensions and make the independence seekers sure to go ahead with the secession plan.
The region has about 5.5 million eligible voters, and polls consistently show the region's inhabitants favour a referendum but are roughly evenly divided over independence from Spain.