“More than 68 teams from more than 45 countries are on standby,” Elisabeth Byrs, spokeswoman of the UN Office for the Coordination of Humanitarian Affairs (OCHA) said.

The search and rescue teams, mobilized under a UN disaster response network, are monitoring the situation and ready to help, she explained.

US President Barack Obama said Friday that a second US aircraft carrier was heading to Japan to provide assistance. Obama said he offered condolences to Japan’s Prime Minister Naoto Kan and promised “whatever assistance is needed.”

A huge surge of muddy seawater filled with rubble and debris — some of it on fire and belching smoke — raced through neighborhoods and across rice fields, footage showed in Miyagi prefecture.

Rows of houses floated bizarrely, resembling whole neighborhoods, through the apocalyptic scenes, while a huge whirlpool of icy seawater in the Pacific Ocean was seen from the air pummeling boats sucked into the maelstrom.

As the death toll climbed into the hundreds and the world looked on in shocked disbelief, the scale of the horror kept unfolding with reports of a missing train, passenger boats and a bursting dam flooding yet more homes. The quake that triggered the tsunami tore cracks into roads, pushed manhole covers and their attached pipes out of the ground like small towers, collapsed roofs and dumped the contents of supermarket shelves on the ground.

Completing the apocalyptic scenes, elsewhere in Japan scores of fires broke out as gas mains were severed. An oil refinery was ablaze in Chiba prefecture outside Tokyo, belching acrid smoke into the skies.

As aftershocks kept rocking Japan, the army sent or readied to deploy thousands of troops and hundreds of ships and planes to help those in need, a desperate rescue effort that became more complex as the cold night fell.

A ship carrying 100 people was swept away by the tsunami, Kyodo news agency reported. It said the death toll was likely to cross 1,000.

A small radiation leak could occur at Fukushima nuclear plant, Japan’s trade minister said, after officials said a pressure build-up had occurred in one of the reactors after the quake. The quake caused an outage that disabled the reactor’s cooling system, triggering evacuation orders for about 3,000 residents as the government declared its first-ever state of emergency at a nuclear plant. Plant workers are scrambling to restore cooling water supply at the plant but there is no prospect for immediate success.

The temblor brought super-modern Tokyo to a standstill, paralyzing trains that normally run like clockwork and stranding hordes of commuters carrying mobile phones rendered largely useless by widespread outages. The quake shook buildings in the capital, left millions of homes across Japan without electricity, shut down the mobile phone network and severely disrupted land line telephone service. It brought Tokyo’s train system to a halt, choking a daily commuter flow of more than 10 million people.

Tsunami waves caused surges along California’s coast that shook some boats loose from docks, as beach-area residents evacuated to higher ground. A half-meter wave hit Mexico’s northwest coast having swept thousands of miles across the Pacific Ocean. Active waves similar to any stormy day on the coast were the only sign that a tsunami had arrived in Washington.