The search for the missing Malaysia Airlines (MAS) flight MH370 entered its 33rd day today with the deployment of 11 military aircraft, four civil aircraft and 14 ships covering an area of about 75,423 square kilometres in the southern Indian ocean.

It has become a race against time as the battery of the black box is expected to last for only 30 days and at the most a few days more before transmission stops completely.

On Monday, the Australian Defence Vessel (ADV), Ocean Shield, which had picked up a pulse signal on Sunday, detected another two signals, while the Chinese ship Haixun 01, heard two signals on Friday and Saturday.

In a statement here today, the Joint Agency Coordination Centre (JACC) said that the centre of the search area was 2,261 kilometres northwest of Perth.

The agency said the underwater search continued with ADV Ocean Shield at the northern end of the defined area, while Haixun 01 and HMS Echo combed the southern end.

Flight MH370, carrying 227 passengers and 12 crew, left the KL International Airport at 12.41 am on March 8 and disappeared from radar screens about an hour later, while over the South China Sea. It was to have arrived in Beijing at 6.30 am the same day.

A multinational search was mounted for the aircraft, first in the South China Sea and then after it was learnt that the plane had veered off course, along two corridors - the northern corridor stretching from the border of Kazakhstan and Turkmenistan to northern Thailand, and the southern corridor, from Indonesia to the southern Indian Ocean.

Following an unprecedented type of analysis of satellite data, United Kingdom satellite telecommunications company Inmarsat and the UK Air Accidents Investigation Branch (AAIB) concluded that Flight MH370 flew along the southern corridor and that its last position was in the middle of the Indian Ocean, west of Perth.

Malaysian Prime Minister Datuk Seri Najib Tun Razak then announced on March 24, seventeen days after the disappearance of the Boeing 777-200ER aircraft, that Flight MH370 "ended in the southern Indian Ocean".