"We must do our utmost for the people of Myanmar," he told reporters in the Thai capital, Bangkok, before departing for Yangon.
"This is a critical moment for Myanmar. The government itself acknowledges that there has never been a disaster on this scale in the history of their country."
Ban also pressed the government to allow large-scale international aid for the 2.5 million people left destitute after the storm.
"I hope your people and government can co-ordinate the flow of aid so the aid work can be done in a more systematic and organised way," he said on Thursday.
By the military government's own count, at least 78,000 people were killed and 56,000 remain missing from Cyclone Nargis, which swept through the country, formerly known as Burma, early this month.
Asda Jayanama, the former Thai first secretary to Myanmar, told Al Jazeera that it was a "symbolic, but also substantive" visit by Ban.
"The fact he has entered Myanmar and engaged with the authority and regime is very important," he said.
"I think that from now on, things can only get better. To what extent, we have to see. That will depend on a number of factors, including a change in attitude of the regime, the UN, and Asean."
Ban said the relief programme was "functioning", but so far "only about 25 per cent of the people in need", have been reached.
The UN says survivors of the storm face hunger, homelessness and potential outbreaks of deadly diseases, especially in the low-lying delta.
Debbie Stothard, head of the South-East Asian human rights group Altsean, told Al Jazeera that the visit by Ban - the most senior international official - was the "last resort" by the world body and a lot of hope was riding on his visit that aid access would be improved.
The democracy activist heading the alternative Asean network that works on issues to do with Myanmar said there had to be an international presence on the ground to ensure that aid is delivered and monitored in a transparent way as "Burma is one of the most corrupt countries in the world".
"The military regime has to understand that it cannot get something for nothing - it must compromise," she said.
She added that if the international community accepts the situation where only a trickle of aid reaches the people, then it is accepting that huge numbers of people will die.
Myanmar's military government was slow to open up to material assistance after the disaster.
And while it has agreed to allow in aid efforts co-ordinated by the regional Association of South-East Asian Nations (Asean) group, it still appears reluctant to accept more than a handful of experienced foreign rescue and disaster relief workers.
On Wednesday, Myanmar announced that it would not accept aid from US warships and military helicopters waiting off the coast of the country, although it said it would allow UN helicopters to begin delivering food to survivors.
|The UN says only a quarter of those in need |
have received any international aid [AFP]
A statement carried in Myanmar's state media said aid carried on US warships had "strings attached".
US naval vessels have been waiting offshore for several days, prepared to airlift medical supplies, food and emergency shelter to regions devastated by the cyclone.
"The strings attached to the relief supplies carried by warships and military helicopters are not acceptable to the Myanmar people. We can manage by ourselves," the state-run New Light of Myanmar newspaper said on Wednesday.
However, it added that other forms of US aid were welcome.
The US is presently airlifting supplies to Yangon, Myanmar's former capital, from Thailand on C-130 cargo aircraft at a rate of about five flights a day.
But transporting supplies from Yangon to the hard-hit Irrawaddy delta is proving difficult.
Myanmar has said it will allow nine helicopters from the World Food Programme to begin operations in cyclone-hit areas that had so far been largely inaccessible.
The government says losses from the storm have exceeded $10bn and on Sunday Ban is to co-chair a donors' conference in Yangon organised by Asean.
The US, however, has questioned the relevance of the fundraising conference, saying it is more important for Yangon to increase access to disaster-hit areas.
"Without an adequate and independent assessment of the situation and current needs, as well as a commitment by the regime to provide the necessary access, a pledging conference is unlikely to produce the results we seek," Scot Marciel, the US envoy to Asean, told a congressional hearing in Washington on Tuesday.
Source: Al Jazeera and agencies