North Korea has toughened its line on people who try to flee across the border into China, a new report by a rights watchdog says.
A protest in Seoul last month over treatment of would-be defectors
Human Rights Watch says that even those who are trying to cross the border for the first time face years in prison.
It says repatriated escapees can spend up to five years in political prison camps and are beaten and starved.
The group says the North Korean government "persecutes its citizens for simply trying to survive".
North Korea has so far made no comment on the report.
"North Koreans are crossing into China to avoid starvation since their government is either unwilling or unable to feed them," said Sophie Richardson, deputy Asia director at the New-York based rights group.
It spoke to 16 North Koreans who had crossed into China between mid-July and early December 2006, just a few of the estimated 200,000 who aid agencies believe may have entered the country.
Many hide in China's north-east as Beijing regards them as illegal immigrants rather than refugees and sends them back to North Korea.
In North Korea's prisons, the report found, inmates face frequent beatings by guards and collective punishments for groups of cellmates.
Punishments include being forced to hit their own heads against the bars of their cell.
"Most of them died after eating the corn stalk powder they gave us and suffered from diarrhoea for about a week," one female former detainee told the group.
"So many inmates died that they wrapped the bodies in plastic and buried them in the mountain," she said.
Those who successfully escaped said the government had been warning of harsher prison sentences as early as 2004.
Before then, the authorities had been more lenient on those who tried to escape, releasing many after questioning or sending them to a labour re-education facility for several months.
The policy change is said to have come about following South Korea's 2004 decision to fly some 400 North Korean refugees from Vietnam to South Korea.