Police said no arrest has been made but an investigation has begun.
The doctors were working at the Potiskum general hospital in Yobe state, Channels TV said.
The gunmen are suspected to be part of the Boko Haram sect, Channels TV reported.
Several Korean experts, including the victims, have been offering help in various fields in Yobe state, Channels TV said.
The incident comes after nine female health workers involved in immunization programs were shot to death in separate attacks Feb. 8.
Police said men riding three-wheel motor vehicles were responsible for those attacks.