Chinese ships defy Vietnam's demand to vacate gas field area.

A Chinese research ship and five escort vessels were spotted in Vietnam's exclusive economic zone (EEZ) close to gas blocks operated by Russian firms in the South China Sea, a day after Vietnam urged the ships to leave. China claims most of the energy-rich waters of the South China Sea, including areas that are within Vietnam's EEZ. The incursion represents a worrying escalation, according to experts.