The son of Philippines President Rodrigo Duterte was cleared on Wednesday of any involvement with a shipment of methamphetamine which was smuggled into the country, the Office of the Ombudsman of the Philippines said.

Paolo Duterte, 43, had been named as one of the middle-men in the receipt of a shipment of 604 kilograms (1331 pounds) of methamphetamine hydrochloride from China, worth around $125 million.

"The complaints against former Davao City Vice Mayor Paolo Duterte and Attorney Manases Carpio were dismissed for lack of basis," the Office of the Ombudsman said in a statement.

Attorney Carpio is married to the president's daughter, Sara Duterte.

The shipment entered the country with the alleged complicity of the customs service and was subsequently seized by the police.

The incident garnered a lot of media attention in the country, where authorities have cracked down on the illegal narcotics trade since Rodrigo Duterte came to power in June 2016.

Thousands have been killed in police raids and extra-judicial operations against alleged drug dealers and users.

The investigation into the potential involvement of two of the president's relatives was based on statements by two customs officials and Senator Antonio Trillanes, one of Duterte's fiercest critics.

After a preliminary investigation, a Senate Committee concluded in August last year that there was no evidence to implicate Paolo Duterte in the drug-trafficking operation. The ombudsman's ruling on Wednesday fully clears him of any wrongdoing.

Having pledged to cripple the country's rampant illegal drug trade during his successful election campaign, upon taking office in June 2017, the Philippine leader promised that he would resign if it was proved that any member of his family was linked to the drug trade.

Filipino authorities say that over 7,000 people have died in the so-called "war on drugs", while international rights groups such as Human Rights Watch estimate that over 12,000 have been killed.