Washington: US President Barack Obama said that the United States has delivered coolant to Japanese nuclear power plant, which broke down in the wake of the massive earthquake.

Tokyo declared a state of emergency for five of its nuclear reactors at two atomic power plants in northeastern coast of Japan, where an 8.9-magnitude quake struck on Friday.

The safety of Japan's nuclear plants also came up when Obama telephoned Japanese Prime Minister Naoto Kan.

"When I spoke to Prime Minister Kan, I specifically asked him about the nuclear plants and their potential vulnerability as a consequence of the earthquake. He indicated that they are monitoring the situation very closely," Obama said.

"So far, they have not seen evidence of radiation leaks. But, obviously, you've got to take all potential precautions," he said.

The coolant was rushed to Japan as US moved its naval and air assets along with humanitarian relief material for the tsunami-hit areas of the country.

"We just had our Air Force assets in Japan to transport some really important coolant to one of the nuclear plants," Secretary of State Hillary Clinton announced.

Japan is very reliant on nuclear power and they have very high engineering standards, but one of their plants came under a lot of stress with the earthquake and did not have enough coolant, she said.

"So Air Force planes were able to deliver that. So we're really deeply involved in trying to do as much as we can on behalf of the Japanese and on behalf of US citizens," Clinton said.

Air, naval aid pours in

Obama said he has dispatched a second ship to the region for possible relief and rescue operation. "We currently have an aircraft carrier in Japan, and another is on its way.

We also have a ship en route to the Marianas Islands to assist as needed," he said.

The Department of Defence said the US Pacific Fleet ships in the Western Pacific were converging in Japan to be in the best position to help those in areas damaged by the massive earthquake and subsequent tsunami.

They included the aircraft carrier USS Ronald Reagan (CVN 76), which departed Southern California waters on March 5 for a regular scheduled deployment to the Western Pacific and US Central Command area of responsibility.

Reagan is the flagship of the Ronald Reagan Carrier Strike Group, which includes USS Chancellorsville (CG 62) and USS Preble (DDG 88). These ships were headed to Honshu's east coast.

"It is too early to say what they will be tasked with once they arrive," the Defence Department said. "We obviously have huge sympathy for the people of Japan, and we are prepared to help them in any way we possibly can," Defence Secretary Robert Gates said in a statement.

"It's obviously a very sophisticated country, but this is a huge disaster and we will do all, anything we are asked to do to help out," he said.