A huge convoy of about 20 road trains laden with 2,000 bales of hay is en route from outback Western Australia to drought-stricken farmers in New South Wales.

The massive cross-country aid effort, organised by the Rapid Relief Team (RRT) charity, includes 1,000 tonnes of hay worth $500,000 which is enough to feed 1,000 cows or 20,000 sheep for a fortnight.

About 16 trucks left Northam in WA's Wheatbelt early on Monday, with the remaining trucks to join them along the route.

The convoy will travel across the Nullarbor, a journey of more than 3,500 kilometres, arriving in Condobolin in NSW's Central West on Friday.

RRT spokesman Alex Sharpe said it had taken less than a week to put the aid convoy together.

"We've done a ring around and we've gotten trucks from people we knew and [from] people who knew people and rattled up some trucks and farmers and hay suppliers and it's come together quite quickly," he said.

Mr Sharpe said communities, farmers and businesses had rallied.

"It's amazing I can say with certainty that everyone involved is absolutely passionate and keen to be on board," Mr Sharpe said.

"Some of the drivers are donating their time, some are doing a route they wouldn't normally do, others are driving for companies but in most cases they've personally put their hand up."

He said many WA farmers had their own memories of drought and were greatly sympathetic to the plight of farmers on the east coast.

"We've seen a lot of fairly emotional people out there this morning that are talking first-hand about their drought experiences," Mr Sharpe said.

Managing director of trucking firm Watsons Logistics and Transport Robert Watson said his company had donated two trucks full of hay, about 80 tonnes, to the convoy.

"There's not much we can do from Western Australia usually, but this is something we can do so we put our hand up," he said.

He said it was important that WA do its part in helping those in the east.

"It's Australia and everyone gets together and helps out," he said.

NSW last week announced "100 per cent" of the state was in drought, with almost a quarter of that in intense drought.

Autumn was the driest on record for many past of NSW and it was the driest July for parts of the central west.