(Updates China death toll, writes through)

HANOI, Nov 3 (Reuters) - Vietnamese authorities warned on Monday of disease outbreaks, including cholera and dengue fever, after heavy rain triggered floods that have killed nearly 100 people in northern and central Vietnam and southwestern China.

At least 65 were killed in Vietnam, and 34 in southwestern China, from flooding and mudslides.

At least 18 people were killed in Hanoi in what is believed to be the heaviest flooding in the capital since 1984, state media said. Schools were closed on Monday as many streets in downtown Hanoi and the city's outskirts remained submerged.

In southwestern China's Yunnan province, the death toll from mudslides caused by heavy rain rose to at least 26, with 45 missing, Chinese state media reported.

The Health Ministry alerted all clinics in flood-hit areas to be staffed around the clock to prepare for any outbreaks, state media reported on Monday.

Up to 500 mm (19.7 inches) of rain has fallen on Hanoi since Friday as well as triggering landslides that have eroded many sections of the north-south Ho Chi Minh highway in Thua Thien-Hue province.

Much of Hanoi got a respite from heavy showers on Monday but the government warned that more downpours, flash floods and landslides could be in store in mountainous provinces in the country's north-central region this week.

"Large-scale flash floods on the rivers, streams and landslides are expected in the mountainous areas from Thanh Hoa to Nghe An," the national weather forecast centre said in a flood report, referring to two provinces.

The Vietnamese government has ordered the army to mend damaged river dykes in northern provinces and to help evacuate people from areas vulnerable to landslides and flash floods.

State media said the lives of thousands were threatened after a dyke broke in Ninh Binh province. It gave no further details.

Vietnam's main agricultural area, including the Central Highlands coffee belt and the Mekong Delta rice basket, have not been affected by the floods, although rain disrupted coffee harvesting last week.

Torrents of mud and rocks hit near the city of Chuxiong in Yunnan province at the weekend, toppling or damaging nearly 1,000 houses, China's Xinhua news agency said. Yunnan is dominated by steep terrain and many of its farmers live in villages on steep slopes. There is also mining in some areas.

Mountain torrents triggered by heavy rain hit Pingguo county in Guangxi to the east of Yunnan, killing eight. (Reporting by Nguyen Nhat Lam and Lucy Hornby; Editing by Louise Ireland)

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