China and Russia on Friday rapped US plans to put a missile defence system on the Korean peninsula, less than 24 hours after Pyongyang twice tested rockets thought to be capable of reaching American territory.

A series of missile tests and nuclear blasts by North Korea have pushed Seoul into talks with Washington about deploying the United States' sophisticated Terminal High Altitude Area Defence System (THAAD), which fires projectiles to smash into enemy missiles.

Beijing fears that the presence of more US hardware on its doorstep will further tip the balance of power in the Pacific towards Washington.

"We both are gravely concerned about the US's likely deployment of the THAAD system in South Korea," Chinese Foreign Minister Wang Yi said at a briefing with his visiting Russian counterpart Sergei Lavrov.

"The move goes beyond the actual defence needs of relevant countries," Wang said.

"It will directly affect the strategic security of China and Russia respectively if it is deployed," he added.

Lavrov condemned Washington for using the North's tests as "an excuse, as a pretext" to deploy what he called Washington's "global antiballistic missile defence".

This week's North Korean rocket tests failed, but Pyongyang has now made three bids in two weeks to test-fly a Musudan missile, which is capable of striking US bases on the Pacific island of Guam.

"The current situation on the peninsula is indeed in a highly dangerous period," Wang said.

He added that proper implementation of UN resolutions barring the North from developing any ballistic missile-related technology is key to bringing the country to the negotiating table.

China is the North's biggest trading partner and its key aid provider.

South Korean military officials say the North is desperate to register a successful launch ahead of next week's ruling party congress, at which leader Kim Jong-Un is expected to take credit for pushing the country's nuclear programme to new heights.

In recent months, the North has claimed a series of major technical breakthroughs in developing what it sees as the ultimate goal of its nuclear drive -- an intercontinental ballistic missile capable of delivering a warhead to targets across the continental United States.

The achievements trumpeted by Pyongyang have included miniaturising a nuclear warhead to fit on a missile, developing a warhead that can withstand atmospheric re-entry and building a solid-fuel missile engine.

Last Saturday, it successfully tested a submarine-launched ballistic missile -- a move that was promptly condemned by the UN Security Council.

Lavrov also backed Beijing's stance that territorial disputes in the South China Sea "should not in anyway be internationalised" and should be resolved by direct negotiations between countries.

An international tribunal is expected to rule soon on a case brought by the Philippines over the issue, which has seen tensions mount between Beijing and Washington.

China claims nearly all the strategically vital sea, despite completing claims from Southeast Asian neighbours including the Philippines, Vietnam, Malaysia and Brunei.