BEIJING/SEOUL (REUTERS) - China's Spring Airlines Co plans to fly to the North Korean capital Pyongyang next year, making it the third airline to run scheduled flights to the isolated country.

The budget carrier hopes to launch four flights a week from its hub, Shanghai's Pudong airport, in early Feb 2016, although the proposal is pending approval from both the North Korean authorities and the Civil Aviation Administration of China (CAAC), a Spring Airlines spokesman said.

China is North Korea's biggest trading partner and diplomatic ally.

North Korea's state airline, Air Koryo, runs regular flights between Pyongyang and Beijing and occasionally operates seasonal routes to Shanghai, Kuala Lumpur and Vladivostok. Air China Ltd operates two flights a week to Pyongyang, three in the summer.

"Air Koryo had launched some charter flights to North Korea previously, targeting leisure travellers and demand seemed to be pretty strong," the Spring Airlines spokesman said on Tuesday. He declined to be named as per company policy.

While North Korea does not publish tourist numbers, travel agencies estimate as many as 6,000 Westerners visit North Korea every year, compared to just 700 a decade ago.

The vast majority are from China, which shares borders with North Korea: the latest available Chinese data shows that 237,000 tourists went to North Korea in 2012, nearly double 2010 levels.

The spokesman for Shanghai-based Spring Airlines said he could not comment on whether the North Korean government had introduced any restrictions on the nationality or origin of tourists on the flights.

North Korean leader Kim Jong Un, who took power in 2011 when his father Kim Jong Il died, has stepped up investment in tourism infrastructure, including the construction of a new airport terminal and a ski resort on the east coast.

Last year, North Korea reopened some of its domestic scheduled air routes for the first time in years.