BEIJING (Reuters) - China will offer its first regular civilian cruises to the Spratly Islands in the South China Sea by 2020, state media said on Wednesday, a move likely to irk other claimants to the disputed waters.

China's activities in the contested area, such as building artificial islands, airfields and other military facilities, have fueled tension in Southeast Asia, although it says most of the construction is for civilian purposes.

The island province of Hainan will operate regular trips to the Spratlys, which China calls the Nansha Islands, in response to increasing demand, the official China Daily newspaper said, citing provincial authorities.

"The province plans a pan-South China Sea cruise line and cruise trips business covering countries along the Maritime Silk Road," it added, referring to President Xi Jinping's initiative to boost investment and trade links.

The trips will begin before 2020, the paper said.

The plans are also likely to irritate the United States and its regional allies, which have voiced concern over China's assertiveness in the busy waterway, where rival claimants have encouraged a civilian presence on disputed islands.

Asked if the cruises might exacerbate tension, Foreign Ministry spokeswoman Hua Chunying said she did not know any details, but it was normal for Hainan to develop its tourism industry in Chinese territory.

"There's no need to read to much into it," she told a daily news briefing.

China claims 90 percent of the potentially energy-rich South China Sea. Brunei, Malaysia, the Philippines, Vietnam and Taiwan lay claim to parts of the sea, through which ships carrying about $5 trillion of trade pass every year.

Since 2013, China has run cruises to the Paracels, known as the Xisha Islands in Chinese. China has controlled the Paracels, which are nearer its coast than the Spratlys, since the 1970s.

State-owned China COSCO Shipping Corp plans to launch cruise trips to the Paracels from next month.

Analysts say China's development plans in the more distant Spratlys would give Beijing its first permanent presence deep in the maritime heart of Southeast Asia.

Beijing has said it wants to build Maldives-style resorts around the South China Sea.

It is unclear if foreigners would be allowed to visit. Only Chinese nationals have so far been permitted to take the island tours.

(Reporting by Michael Martina and Ben Blanchard; Editing by Clarence Fernandez)