BEIJING — China confirmed Thursday that it is building a second aircraft carrier, a move that will probably raise further concerns in the West and among its neighbors over Beijing’s assertive moves in the South China Sea.

The carrier will be designed in China and built in the port of Dalian, said Yang Yujun, a spokesman for the Defense Ministry. It will have a displacement of 50,000 tons – significantly less than the largest U.S. carriers – and will carry China’s J-15 fighters. The carrier will have a ski-jump-style takeoff.

“China has a long coastline and a vast maritime area under our jurisdiction. To safeguard our maritime sovereignty, interests and rights is the sacred mission of the Chinese armed forces,” Yang told reporters.

China claims almost all of the South China Sea, a vast and strategically important sweep of islands and shipping lanes.

These claims are a major source of tension with the United States, as well as with many Asian neighbors including Japan, Vietnam and the Philippines. China and Japan also have sparred over the East China Sea.

Yang did not release more details nor did he say when the carrier would be completed. Information about the program is closely guarded.

China already has one aircraft carrier, the Liaoning. It was purchased from Ukraine in 1998 and retrofitted domestically.

Plans to build a second carrier do not come as a surprise. Rumors have been swirling for more than a year, but have been quickly scrubbed by China’s censors.

In February, an overzealous city government leaked news that it had been selected to supply electronic components for a new carrier, only to see the good news deleted.

Photos released by IHS Jane’s Defence Weekly in October showed what some thought was an aircraft carrier under construction in Dalian, the port where the Liaoning was refitted.

The Pentagon’s 2015 report on military and security issues in China predicted the country could “build multiple aircraft carriers over the next 15 years.”

Building a second carrier is part of Beijing’s plan to increase its naval presence as it modernizes its military. The country’s officially disclosed military budget – still small compared with that of the United States – has grown by double digits for nearly two decades, up 10 percent this year to $141 billion.

The Pentagon has long held that China is within its rights to improve its military, but there are points of friction.

The U.S. military has conducted a number of freedom-of-navigation operations, as they are known, in international waters in recent months, in an effort to make sure shipping lanes remain open to traffic in areas such as the South China Sea.

Adm. John Richardson, the chief of the Navy, said recently that Russia and China are world powers, and the United States must make sure it stays ahead of both with military technology. He called China more of a “quantitative threat,” a nod to its military’s growing capacity.