Najib credited their release to cooperation between Malaysian and Philippine security forces, and said no ransom was paid.
Malaysian officials earlier said the kidnappers had demanded a ransom of 500 million pesos (USD 11.4 million) for the Chinese hostage.
Gunmen, believed to be Philippine Abu Sayyaf militants, kidnapped the 28-year-old Shanghai woman and the 40-year-old Filipino woman from the Singamata Reef Resort in the eastern Malaysian state of Sabah on April 2. They were believed to have been taken to the southern Philippines.
He said authorities were working to return the Chinese woman to her home country as soon as possible.
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Najib didn't give further details and officials couldn't immediately be reached for comment.
Two Philippine security officials who have been monitoring kidnappings in the south confirmed the two women had been released by Abu Sayyaf militants in Parang township in the southern Philippine province of Sulu after a series of negotiations.
The two were served lunch by local police and then escorted out of Sulu on board a speedboat back to Sabah, said the officials, who spoke on condition of anonymity because they were not authorized to talk to the media.
Misaya's group has been blamed for other kidnappings in the poor, predominantly Muslim province.