Chinese President Xi Jinping holds talks with his Philippine counterpart Rodrigo Duterte in Manila, the Philippines on Nov. 20, 2018.Chinese President Xi Jinping holds talks with his Philippine counterpart Rodrigo Duterte in Manila, the Philippines on Nov. 20, 2018.

The Philippines and China have been warming up.

Observers will be watching closely to see what the new leadership will mean for the Philippines, as they head to the polls on May 9.

There are good reasons why foreign policy should be a hot button issue in the Philippines elections, according to an associate professor of international studies at De La Salle University.

There are compelling reasons why a president's preference for a particular country at the expense of other partners has ramifications beyond one administration, according to a report published.

The Philippines became a military ally of the U.S. in 2016 after the president declared his country's separation from the US. He wanted closer ties with China.

Much of Beijing's promised infrastructure investments have not materialized, so he has had little to show for his China pivot.

The South China Sea is where the Philippines and China have conflicting territorial claims, and where China has continued incursions into parts of the sea that are internationally recognized as belonging to the Philippines.

Anti-China rhetoric within Durterte's own government has grown louder, while opinion polls show that the Philippine public is skeptical of Beijing. Analysts said that sentiment could push the next president away from the China-pivot.

CNBC looked at where the top Philippine presidential candidates stand on the issue of China based on their comments on the campaign trail.

Marcos Jr., the son of the late dictator Ferdinand Marcos, is one of the top candidates. Francisco Domagoso is the current mayor of Manila.

Marcos is seen as the most China-friendly candidate. According to the latest survey by a pollster, Marcos is the favorite in the presidential race.

The 2016 ruling on the South China Sea dispute between China and the Philippines is one of the more controversial issues in the relationship. Specific portions of the sea that China and the Philippines claimed were ruled out by the international tribunal.

The ruling was rejected by China. In pursuit of closer ties with Beijing, the man was criticized for not doing more to demand Beijing's compliance.

In a series of media interviews in January, Marcos said he was willing to set aside the 2016 ruling to engage with China.

The former senator and congressman appeared to have changed his stance in a debate. He wants the Philippines to have a military presence in the South China Sea to show China that we are defending our territory.

Marcos said he would not prioritize a military resolution to his country's dispute with China and would continue pursuing engagement with China.

Leni Robredo, who is also vice president, has been more steadfast in advocating a tougher stance against China.

In the Philippines, the president and vice president are elected separately. Robredo was a critic of the drug war and resigned from the cabinet.

She was seen as the anti-Duterte candidate by 15% of the respondents in a survey.

According to reports, Robredo said she would pursue a foreign policy that doesn't favor any countries.

She emphasized the need to recognize the 2016 ruling on the South China Sea dispute before the Philippines and China can explore any joint oil and gas exploration projects.

The vice president favors stronger ties with the U.S. and other countries, such as the Philippines and Southeast Asian neighbors.

The current mayor of the Philippine capital city of Manila is Francisco Domagoso, a former actor.

Domagoso, better known by his screen name Isko Moreno, is seen by political analysts as a centrist candidate that has sought a middle ground on issues including foreign policy.

The mayor of Manila is said to be in agreement with Robredo on the need to assert the 2016 ruling.

Local media reported that Domagoso would back joint oil and gas exploration deals with China if the Philippine government awarded them.