Assistant foreign affairs minister Tim Watts is urging Australian citizens to leave war-torn Sudan now, as "plenty of seats" have been secured on flights out of the country.

The Department of Foreign Affairs (DFAT) said 102 Australians had left Sudan but 142 still remained.

An extended ceasefire in the African nation ends on April 30 and the federal government is unable to guarantee flights out afterwards.

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The minister's statement comes after an Australian man, who has now landed in Melbourne after fleeing Sudan, criticised the federal government for not doing enough to help its citizens get to safety.

Watts said it was a "dangerous and volatile" situation in Sudan at the moment.

"Our message to any Australians leaving the country is clear, this ceasefire is your opportunity.

"If it is safe for you to get to the Wadi Sayyidna airport, leave now.

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"We can not guarantee there will be flights leaving after the conclusion of this ceasefire on April 30.

"There are plenty of seats for Australians leaving from that airfield and you will be met with Australian consular officials to help assist you with your journey on to Australia."

He said DFAT officials had been working "around the clock" to secure seats on flights operated by partner countries exiting Sudan.

"We are also securing seats on road convoys leaving the country."

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