The warning comes after a major aid group told Al Jazeera that hundreds of thousands of survivors from Cyclone Nargis are facing a potentially "apocalyptic" threat from water-borne diseases.
Tim Costello, the CEO of Australian charity World Vision, told Al Jazeera there were already signs that diseases such as dysentery, diarrhoea, dengue fever were starting to take hold.
Speaking from Yangon, he said the group's relief workers in the hard-hit Irrawaddy delta were "gravely worried that we are tottering on the edge of this epidemic breaking out."
"If it does, its lethal effects will be apocalyptic," he said.
On Tuesday the United Nations' emergency relief arm warned Myanmar will "face a catastrophe of monumental proportions" unless aid efforts match the scale deployed during the Asian Tsunami.
Aid groups say the first 10 days are critical in getting relief to survivors of any disaster, but almost two weeks on that window has now closed for people in Myanmar.
With the death toll from Nargis already topping 34,000, there are reports of soldiers blocking foreign aid workers from reaching some of the worst-hit areas.
The military has taken control of foreign aid supplies, and there are suspicions that relief supplies are being misappropriated after victims reported they are receiving poor quality food.
The bulk of the aid supplies that have been cleared to land in Myanmar are reported to be stuck on planes at Yangon airport, which does not have the lifting equipment needed to unload it.
As a result the few aid agencies allowed to operate in Myanmar say they have only reached a third of the one million people left homeless by the cyclone.
On Wednesday Thailand's prime minister left for Myanmar to reportedly pressure the military government to allow international aid workers in by urgently issuing their visas.
Samak Sundaravej declined to comment to waiting reporters except to say that he had plans to meet his Myanmar counterpart, Thein Sein, in Yangon.
The trip comes after last week's failed attempt by the Thai PM, who was responding to requests from the US, Britain and the UN, to act as mediator with Myanmar's leaders.
Samak's delegation was also carrying medical supplies and satellite phones to donate to relief efforts, according to Thai officials.
'Race to save lives'
Speaking to Al Jazeera World Vision's Tim Costello said it time to put aside political considerations and focus urgently on the humanitarian need.
|Aid agencies say signs are growing of |
potentially deadly epidemics [GALLO/GETTY]
"This is not a time for politics. It's a time to race to save lives."
He said in any humanitarian crisis it was important to make sure that aid is channelled directly to international aid agencies and not to the government.
"[But] the truth is that both the Australian and US governments could only negotiate their flights in on the basis that [aid] went to the military," he said.
"My staff are in tears of frustration, even guilt … that they haven't got aid to people who are waiting for it.
He said aid workers have to keep pushing through despite the "really, really narrow parameters in which we operate".
Costello said despite the overall gloomy scenario, there were indications that the UN may be able to get visas for 20 experts to coordinate emergency water and sanitation supplies and help prevent of epidemics breaking out.
On Tuesday the UN aired its "increasing frustration" at being barred from helping the neediest survivors, saying the crisis in Myanmar's remote, flooded south posed an "enormous logistic challenge".
Elisabeth Byrs, a spokeswoman for the UN's emergency relief arm, in warning of a "second catastrophe", said it needed "at least an air or sea corridor to channel aid in large quantities as quickly as possible".
But the military government of Myanmar has said that the needs of the people after the storm "have been fulfilled to an extent".
Vice-Admiral Soe Thein, a government spokesman, told the New Light of Myanmar newspaper: "The nation does not need skilled relief workers yet."