Crews will resume the underwater hunt for missing Malaysia Airlines flight MH370 at the end of September, moving the search area further south than initially planned, a senior Australian official has announced.

The search had been due to start next week but the first of three ships that will scour a remote patch of the Indian Ocean for the plane that vanished in March needed some additional work done in Indonesia, said Martin Dolan of the Australian Transport Safety Bureau.

The ship, Malaysia's GO Phoenix, is now expected to begin searching on 30 September.

Officials have been refining their analysis of satellite data from the Boeing 777 to get the best idea of where they believe it crashed in the ocean far off Australia's west coast. The most recent analysis suggests the aircraft turned south earlier than previously thought, meaning it may have entered the water in an area south of what was initially considered the highest priority search zone, Dolan said.

The GO Phoenix will therefore begin its search in that southerly stretch of ocean, located along what is known as the "seventh arc", a 23,000 sq mile (60,000 sq km) targeted area where investigators believe the plane ran out of fuel and crashed based on its last signal.

"Our plan has a sequence of priorities," Dolan said. "It's all about probability – we'll start with the highest probability."

The second ship, provided by the Dutch contractor Fugro Survey, is likely to focus on an area south of the GO Phoenix when it eventually arrived, Dolan said.

Flight MH370 disappeared on 8 March after veering off its northerly course from Kuala Lumpur to Beijing for reasons unknown. It is thought to have crashed 1,100 miles (1,800km) off Australia's west coast, but no trace of the aircraft or the 239 people on board has been found.

Two survey vessels have spent months mapping the entire underwater search area, which reaches depths of 3.7 miles (6km). Once the search begins the Malaysian and Fugro ships will slowly tow equipment with side-scan sonar about 100 metres (330ft) above the ocean floor to look for wreckage. The data from these "towfish" will be transmitted in real-time back to crew aboard the ships, who will analyse it for anything unusual.

The search is expected to take up to a year.