At least 20 people were killed in flash floods in several parts of Myanmar over the past week that also affected thousands of others, an official here said on Tuesday.Director of the Department of Social Welfare, Relief and Resettlement U Chun Hayel said severe floods, triggered by heavy rainfall lashing Sagaing and Mandalay regions as well as Kachin and Shan states over the past week, destroyed over 17,000 houses till Monday, affecting nearly 100,000 people, Xinhua reported.Regional authorities were carrying out rescue and relief work in the flood-hit areas, Chun Hayel said.Meanwhile, the weather bureau forecast that central Myanmar areas will experience a continuation or increase of rain in the next two days.The weather bureau has asked fishing boats at sea to be alert to the severe weather conditions.