The officials told Deutsche Presse-Agentur dpa that 18 people were reported killed and nearly 400 homes were destroyed in the south-eastern province of Hadhramout, some 900 kilometres from the capital Sana'a.
In the neighbouring al-Mahra province, on the border with Oman, two people were killed, they said.
Yemeni President Ali Abdullah Saleh ordered the army to assist the rescue and relief operations, the official Saba news agency said.
Saleh also flew to Mukalla, the provincial capital of Hadhramout to oversee the relief and rescue operations, the agency said.
A government committee set up to coordinate rescue efforts declared Hadhramout and al-Mahra disaster zones, Saba said.
Hadhramout Governor Salem al-Khanbashi told state radio that fatalities were reported from different areas of the province, but accurate figures could not be gathered owing to the difficulties of reaching all the affected areas.
He said that among the affected areas were two of the largest historical towns; Tarim and Shibam.
Al-Khanbashi said many towns were isolated by the flood water, and that military helicopters were sent to the most hard-hit areas to support the rescue operations.
Officials in Sanaa said the government also asked foreign oil companies operating in Hadhramout and neighbouring Shabwa province to send their helicopters to help rescue stranded residents.
Civil defence officials said continued heavy rains were hampering rescue operations on Friday. dpa kal wjh ncs
- Deutsche Presse Agentur
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