The women work for the California based-Current TV, an online media outlet founded by Al Gore, the former US vice-president.

They were believed to be on a reporting trip when they were seized after reportedly ignoring North Korean warnings to stop filming from the Chinese side of the border.

The reporters were believed to have been seized near the Tumen river, a common escape route for refugees fleeing the North.

The Tumen river in the east and the Yalu river in the west form most of the border between China and North Korea.

US concern

The US state department has expressed concern over the detentions.

Speaking to the AFP news agency earlier this week, a spokesman for the state department in Washington said US officials were working with Chinese government officials to determine the welfare of the reporters.

"We've also been in touch with North Korean officials to express our concern about the situation," Fred Lash, a US press officer, said.

The US has no diplomatic relations with North Korea and channels of communication between Washington and Pyongyang are limited.