Hanoi invited the diplomatic community to its Russian-built missile-guided frigates docked in Manila Bay at the start of a three-day goodwill visit.
China lays claim to almost all of the entire South China Sea, believed to be rich minerals and oil-and-gas deposits. Brunei, Malaysia, the Philippines, Vietnam and Taiwan also have claims, creating one of Asia's biggest possible flashpoints.
"We are trying to hold joint patrols and operations in the Spratlys, including search-and-rescue operations," said a Philippine naval official, referring to a disputed island chain. He declined to be identified because he was not authorized to talk to the press.
"We are not trying to challenge China's naval superiority in the disputed area. We have no intention to heighten any tension. These are peaceful activities, like sharing of experiences and best practices."
The two 100-meter-(330-ft-) long Russian-built warships are equipped with stealth technology to display a minimal profile on enemy radar screens. They have anti-ship missiles and anti-submarine warfare helicopters.
Concern is growing about an escalation in disputes in the South China Sea even as claimants work to establish a binding code of conduct to resolve them.
"We hope all sides can do more to increase mutual trust and safeguard regional peace and stability," China's Foreign Ministry spokeswoman Hua Chunying told a daily press briefing, when asked about the visit.
China on Monday hit back at "irresponsible remarks" by the United States, which has called on Beijing to stop a land reclamation project on a reef.
"The first port call is a positive and good sign of the improving and deepening relations between the Philippine Navy and Vietnam People's Navy," said Philippine Lieutenant Commander Marineth Domingo.
In March, the two navies held staff-to-staff talks to step up exchanges in intelligence and information, naval technology and training.
Three months later, Vietnamese and Philippine troops got together on a disputed island to play soccer and volleyball and drink beer in a get-together Philippine officials said proved there could be harmony despite a web of overlapping claims.
China dismissed the meetings as a "clumsy farce."
Vietnamese Navy ship Ly Thai To (HQ-012) is seen docked at Manila's South Harbor.