UNITED NATIONS, Aug. 1 (Xinhua) -- The UN humanitarian office said on Wednesday that it is on stand-by to help southeastern Asian countries that are battered by serious flooding caused by monsoon rains.

Seasonal flooding has displaced 148,000 people in Myanmar since July 9 with several UN agencies and nongovernmental organizations providing assistance and assessing further needs, said the UN Office for the Coordination of Humanitarian Affairs (OCHA), based in New York.

Two people were reportedly dead in Cambodia which, along with Thailand, was bracing for more flooding, said OCHA.

"In Cambodia, more than 4,700 families have been affected by flooding with at least two deaths reported," the office said. Rising flood waters in the Mekong River pose a further risk.

"In the Lao People's Democratic Republic, the rains that caused the collapse of the Attapeu Province dam have not yet receded," OCHA said. "Search and rescue operations continue with assistance from the United Nations, the Association of Southeast Asian Nations, many countries and the private sector."

The July 24 collapse killed more than 20 people with well more than 100 reported missing, according to published reports.

Five of Thailand's 76 provinces already have been affected by rising waters from the Mekong River, the office said.

The world organization is working closely with national governments in the impacted areas and providing assistance, OCHA said. "As rains continue in many areas, the risk of further flooding remains acute and the UN is on stand-by to respond as required to assist communities in need."