Panama authorities have seized a North Korean vessel from Cuba that was carrying undeclared weapons hidden in containers of brown sugar, according to Panamanian president Ricardo Martinelli.

The weapons were detected as the ship approached the Panamian port of Manzanillo on Monday night. Authorities were alerted that the ship was carrying drugs but a further search revealed military equipment.

"We're going to keep unloading the ship and figure out exactly what was inside," Martinelli told Panamanian television late on Monday.

Panama's security minister Jose Raul Mulino told CNN the 35-strong North Korean crew resisted arrest and the ship's captain attempted to commit suicide.

Panama will ask a United Nations technical support team to inspect the cargo, according to Mulino.

President Martinelli posted on Twitter a picture of the cargo and said:

"The world needs to sit up and take note: you cannot go around shipping undeclared weapons of war through the Panama Canal."

The pariah state of North Korea is barred from importing and exporting all weapons, with the exception of small arms, in compliance with several United Nations resolutions.