MANILA - Philippine authorities have seized about P6 billion ($120 million) worth of methamphetamines in a series of anti-narcotics operations this month that have yielded the biggest haul in the country's history, the justice minister said on Tuesday.

The National Bureau of Investigation (NBI) conducted the operations, including one on Monday in San Juan City in the capital Manila where drums of chemicals used to produce methamphetamines, or "shabu" as it is known, were seized.

That followed a raid on Friday in a quiet neighborhood in the same city, when six people were arrested and 560 kg of suspected methamphetamines was found, worth an estimated $67 million.

"It is not only the biggest haul this year, but the biggest so far in history," Justice Secretary Vitaliano Aguirre said in a news conference.

The seizures will be a boost for President Rodrigo Duterte, who is facing allegations of widespread human rights violations in a bloody war on drugs dominated by killings of drug users and pushers, with few known arrests of major drug lords.

Duterte has expressed his frustration at the failure of anti-money laundering authorities to chase the trail of drug money, accusing them of helping to fuel corruption and threatening to charge them with crimes.

Agents of the NBI said their latest operation involved an apartment rented by a Chinese national, who was not there when the raid took place.

More than 6,000 people have been killed in the crackdown since Duterte took office in July, roughly a third in police operations. The other deaths are classified as under investigation, many believed to be the work of vigilantes.