By Marius Zaharia

VIENTIANE (Reuters) - Economic growth in ASEAN countries was expected to dip to 4.5 percent in 2016 from 4.7 percent last year due to China's slowdown and uncertainties related to Britain's vote to leave the European Union, the member states said in a statement.

Economic ministers meeting in Laos, which holds the ASEAN chairmanship this year, said jointly that growth in the 10-nation group's $2.4 trillion economy should recover to 4.7 percent next year due to "strong private and public consumption and improved efficiency in infrastructure."

"The region is exposed to ... continued moderation in the Chinese economy, to uncertainties over the new relationship between the UK and the EU after Brexit," the statement said, adding that ASEAN remained committed to further integration.

Import duties on 99.2 percent of tariffs in Brunei, Indonesia, Malaysia, the Philippines, Singapore and Thailand and 90.9 percent in Cambodia, Laos, Myanmar and Vietnam have been eliminated, the ministers said on the integration progress.

About a quarter of the group's total trade of $2.3 trillion is intra-ASEAN. China is ASEAN's top external partner, with 15 percent of the total, followed by Japan, the European Union and the United States.

The countries also said they aim to harmonize economic strategies, recognize each other's professional qualifications, improve custom clearance and intellectual property rules, and close the development gap between the poorer members - Cambodia, Laos, Vietnam and Myanmar - and the rest of the region.

They also agreed to enhance the connectivity of their transportation infrastructure and communications, better facilitate electronic transactions, integrate industries to promote regional sourcing, and enhance private-sector involvement in the economy.

ASEAN's closer economic integration is considered a major step forward from what has been considered since the earliest days of its existence as a political project for peaceful regional relations.

A joint report by AmCham Singapore and the U.S. Chamber of Commerce published on Thursday showed that 53 percent of the U.S. companies thought ASEAN has become more important in terms of worldwide revenue in the past two years. About two thirds said it will become more important in the next two years.

Vietnam, Indonesia and Myanmar were the top destinations for the U.S. companies' expansion plans within the region, with Singapore, Laos and Brunei the least preferred.

Corruption, transparency and good governance remained key challenges for the regional outlook, the report showed.

(Reporting by Marius Zaharia; Editing by Simon Cameron-Moore)