MANILA - President Rodrigo Duterte's decision to "separate" from the United States and enhance its ties with China is "incomprehensible and unwise," a former foreign affairs official said Friday.

"The declared shift away from the US to hastily embrace a neighbor that vehemently rejects international law is both incomprehensible and unwise," former Foreign Affairs Secretary Albert del Rosario said in a statement.

"We must be with nations whose values we share such as democracy, respect for human rights and the rule of law. To stand otherwise is not what Filipinos are- it is not what we do," he added.

Duterte, in Beijing for a state visit, announced Thursday his "separation" from the United States following a bilateral meeting with Chinese leader Xi Jinping.

"I, in this venue, your honors, in this venue, I announce my separation from the United States both in military -- not in social -- both in military but economic," Duterte said, drawing applause from the crowd.

• READ: While in China, Duterte announces 'separation' from US

Apart from hoping to strengthen ties with China, Duterte said he will also talk to Russia's Vladimir Putin.

"I've realigned myself in your [China] ideological flow and maybe I will also go to Russia to talk to (President Vladimir) Putin and tell him that there are three of us against the world - China, Philippines and Russia. It's the only way," he said.

• READ: Duterte: It's Russia, China, PH 'against the world'

This is a dramatic shift of foreign policy under the Duterte administration from that pursued by predecessor Benigno Aquino III, under whom Del Rosario served.

Manila in 2014 took Beijing to an arbitral tribunal over territorial claims in the South China Sea, and won the case in July this year.

China had repeatedly said it will not recognize the ruling, and Duterte, who took office weeks before the decision was out, has said he will not flaunt the outcome.

Duterte had also emphasized in several occasions that he is fed up with Western agenda dictating the country's foreign policy.

On Wednesday, he announced that it was "time to say goodbye" to the US.

"Your stay in my country was for your own benefit. So time to say goodbye, my friend," he said.

"What kept us from China was not our own making. I will charter a new course," he added.