New Zealand Prime Minister John Key will visit China, Vietnam and South Korea in July to further cement New Zealand's strong relations with the Asia region.

Key's visit to South Korea and Vietnam will be his first as prime minister. It will be his second visit to China as prime minister.

"Asia is clearly becoming increasingly important to New Zealand. Strengthening our relationships with the region is a key priority for the government and this visit will further underline our already warm relationships with these three countries," Key said in a statement on Monday.

While in South Korea, Key will hold a summit meeting with President Lee Myung-bak to discuss the current free trade negotiations, security on the Korean Peninsula and Korea's preparations to host the G20 Summit in November.

Key will visit Beijing for formal discussions with China's leaders and will also visit the New Zealand Expo Pavilion in Shanghai to mark New Zealand's "National Day" on July 9.

"The Shanghai Expo is a prime opportunity to grow markets for New Zealand goods and services in China, and to capitalize on New Zealand's unique position as the first developed country with an FTA with China," Key said.

In Vietnam, Key will meet with, among others, the Vietnamese prime minister, president and senior Communist Party representatives.

Key will visit South Korea from July 4 - 7, China from July 7 - 10 and Vietnam from July 10 - 12.