China is "one to two years" ahead of Japan in helping Thailand upgrade its outdated railway network, the Thai deputy prime minister said in Hong Kong on Thursday.

Pridiyathorn Devakula denied recent reports that a Japan-backed line is to become his country's first high-speed railway, adding that Thailand is a "small country" that has to be friendly to China and Japan.

Japan had not yet said whether it would build a high-speed or medium-speed line, he said, noting that Japan would carry out a feasibility study before deciding the speed with Thailand.