In response to the request for International assistance made by the Japanese government, various countries have already dispatched search and rescue teams to Japan.  Some of them have already arrived.  For example, a British group has already landed in Japan.
Two U.S. search and rescue teams have already arrived in Japan.  They are from Fairfax, Virginia and Los Angeles.  After refueling in Alaska, they left for Japan. They landed at an airport near Tokyo. They are being given orders as to where to start searching for survivors. 
USAID determines which search and rescue teams are best suited to respond to the request.  It has been reported that the U.S. sent the two best trained and equipped teams.  " 
The Los Angeles and Fairfax teams are the only teams in the U.S. that are fully  trained and equipped to handle international earthquake relief efforts. USAID is  sending 74 members from the L.A. team to Japan and 72 members from the Fairfax  team, along with rescue dogs and 75 tons of equipment."
To be mobilized first, the Los Angeles Urban Search and Rescue Team is one of the elite emergency team in the whole nation.  That is why it was the first one to be deployed.  It has 178 elite responders who are well trained to function in any emergency situation domestically and internationally.
These U.S. search and rescue teams will be deployed to areas selected by the Japanese Foreign Ministry.  " the 
Japanese  Foreign Ministry has said the United States' emergency teams will most  likely be sent to join rescue efforts in Ofunato, which is in the Iwate  Prefecture of Japan." 
So far, the Japanese government has already deployed thousands of military personnel to the affected areas.  They are finding a lot of dead bodies thus far.  
China has already sent equipment, military manpower and medicine.
Teams with search dogs arrived at Narita International Airport from Germany and  Switzerland, bringing 41 members and three dogs from Germany and 27 workers and  nine dogs from Switzerland. A 15-member Chinese emergency team, the first  dispatched to Japan, and a team of 72 rescuers from the U.S. with search dogs  arrived later today, Sunday.
A team of 45 people from Christchurch, New Zealand  which was hit by an earthquake last month is also expected to arrive in Japan later today.
Russia has experience with dealing with nuclear radiation accidents.  "Vladimir Putin said that Russia is ready to provide up to 150,000 tonnes of liquefied natural gas to Japan and to increase the  supply of coal. 
 Australia, South Korea and other countries have already offered assistance to Japan.