The US says it will also base a military reconnaissance plane at Singapore's Paya Lebar air base. US P-8s already operate from Japan and the Philippines, and surveillance flights have taken off from Malaysia. The P-8 was deployed on Monday, and will remain in Singapore until 14 December.
In addition to the P-8 deployment, the US says it will operate a military plane, either a P-8 Poseidon or a P-3 Orion, from Singapore for the foreseeable future, rotating planes on a quarterly basis.
The US-Singapore agreement, announced after a meeting in Washington on Monday between US Defense Secretary Ash Carter and Singapore Defence Minister Ng Eng Hen, also covers co-operation on counter-terrorism, fighting piracy, and disaster relief.
Speaking at a daily news briefing, Chinese foreign ministry spokeswoman Hua Chunying said the US was "pushing regional militarisation", which did "not accord with the joint long-term interests" of the region.
Despite rising tension with China over its South China Sea territorial claims, a US navy spokesman based in Singapore insisted that the deployments were "not solely focussed on the South China Sea".
"It's not about the South China Sea, it's about partnership with Singapore and other partners in the region," said Lt Commander Arlo Abrahamson, speaking to the BBC.
He pointed to regional co-operation in the search for the missing Malaysian Airlines flight MH370 and the Air Asia plane that crashed on 28 December 2014, as examples of the kinds of operations that would be helped by a base in Singapore.
A US navy statement also said that the deployment was "in support of shared maritime security and HA-DR (High Availability and Disaster Recovery) initiatives in the Indo-Asia-Pacific region."
China claims almost the entire South China Sea, putting it in territorial dispute with several countries, including Vietnam, the Philippines and Malaysia, among others. It has been building islands, equipped with runways, in the area.
China also has a separate dispute with Japan over islands in the East China Sea.
