A British navy submarine has joined up to 10 planes and nine ships in the search for missing Malaysia Airlines Flight MH370 in the Indian Ocean.
Britain's Royal Navy submarine, HMS Tireless, arrived in the vast search area about 1500 kilometres northwest of Perth on Wednesday morning.
British navy vessel HMS Echo was also reached the search zone on Wednesday.
"British nuclear submarine HMS Tireless and survey ship HMS Echo have arrived in search area for #MH370," Britain's High Commissioner to Malaysia, Simon Featherstone, said on Twitter.
While planes, ships and helicopters have been deployed to search for the crashed jet, HMS Tireless is the first submarine to be drafted in to help scour the 221,000 square kilometre search area.
The federal government's Joint Agency Coordination Centre (JACC) said nine military planes would assist in the search on Wednesday, with one civil jet providing a communications relay.
JACC said nine ships would also be out searching.
The weather forecast is for "marginal conditions", with areas of broken cloud, sea fog and isolated thunderstorms, reducing visibility, JACC added.
Malaysian Prime Minister Najib Razak is set to arrive in Perth later on Wednesday before he visits the RAAF Pearce air base, the departure point for the seven-nation air search.
Australian defence vessel Ocean Shield is expected to reach the search zone on Friday with a pinger locator to find flight MH370's black box.
The plane vanished on March 8, with 239 passengers and crew on board, including six Australians and two New Zealanders.
