SHANGHAI, July 4 (Reuters) - Four North Korean teenagers slipped into the British consulate in Shanghai on Friday and requested political asylum, the latest in a string of such defections in Chinese cities.

Two other men from the impoverished Stalinist state fled to South Korea by boat on Friday, a rare case of direct defection. Most refugees arrive in the South through third countries after crossing North Korea's relatively open border with China.

A rights group source identified the asylum seekers in Shanghai as two boys and two girls, aged 15 to 17, who fled from North Korea to northeast China between 1999 and 2000.

The group met reporters in Beijing on Thursday and said they planned to defect, but refused to say where and when.

"When I was in North Korea, I had corn meal three times a day and rice on my birthday," Choe Il, one of the boys, said.

"You are considered rich if you eat like that," added the 15-year-old boy, who said he changed his name to avoid his family being persecuted at home.

The four arrived in Shanghai from Beijing and made the dash for the consulate with the help of ethnic Korean Chinese nationals.

Diplomats said the four walked into the visa section of the consulate and asked for asylum, but declined to provide further details.

"We're still trying to ascertain their identities," a British diplomat said.

Activists say up to 300,000 North Korean refugees are hiding in northeast China after fleeing hunger, poverty and repression in their homeland.

Beijing, a close ally of Pyongyang, has an agreement with its Communist neighbour to repatriate North Koreans, whom it views as economic migrants -- not refugees.

The defectors said they lived in fear, rarely venturing out of their adopted homes in northeast China.

"I couldn't sleep at night," Kim Guang-il, a 17-year-old boy, said. The teenagers declined to have their pictures taken lest their families back home get into trouble.

China allowed more than 130 North Korean asylum seekers who sneaked into foreign embassies and schools in Beijing since 2002 to leave for South Korea via third countries.

Defectors say North Korean refugees who are sent home face imprisonment, torture or death.

In Seoul, the military said it found the two North Korean defectors in a boat off the west coast of the peninsula at 1:30 a.m (1630 GMT Thursday).

The two men, both in their 40s, arrived without any emergency equipment, food or extra clothing, yet appeared to be in stable medical condition, the South's Yonhap news agency reported.

The defectors said they decided to flee to the South after secretly listening to South Korean radio and because of deteriorating living conditions in the North, the agency said. (With additional reporting by Frances Yoon in Seoul)