"We have defined an exclusion zone -- off shore from the Fukushima nuclear power plant -- where vessels are not to enter or transit," said Maersk spokesman Michael Christian Storgaard.
"As long as it is considered safe, Maersk vessels will continue to call Japan." He told Reuters that the exclusion zone was a minimum of 18 miles. "We are monitoring the situation and it might change."
Japan's Fukushima nuclear complex has been torn apart by four explosions since an earthquake and tsunami hit on March 11 and has been emitting radiation.
Maersk is not monitoring radiation levels aboard its ships as of now, but is heeding the bulletins issued by the various Japanese port authorities on the levels of radiation at their ports, said Mary Ann Kotlarich, a spokesperson for Maersk Line in the U.S.
Last week's earthquake and tsunami hit Japanese ports, although shipping companies expect to use other terminals not disrupted by the disaster.
Maersk's main liner services to Tokyo and other larger container ports have not been directly affected by the radiation, but feeder lines serving smaller ports in Northern Japan are likely to be affected, Kotlarich said.
"Number one, can they call the ports? And number two, can they get the cargo if they can get into those ports?" she said.