Thousands of people in Vietnam are suffering a "severe" shortage of fresh water because of drought and salinisation, prompting authorities to declare a state of emergency on Saturday.

A weeks-long heatwave has brought drought and saline intrusion to an area of Tien Giang province, 60 kilometres (37 miles) south of business hub Ho Chi Minh City.

The province's Tan Phu Dong area -- with 12 kilometers of coastline along the East Vietnam Sea, crisscrossed by waterways -- has been particularly badly hit.

Salinisation -- the intrusion of salt water from the sea -- has severely affected crops and thousands of households among the 43,000 people living in the area, the Vietnam News Agency reported.

A state of emergency over the shortage of water for domestic use was announced Saturday for the Tan Phu Dong district, it added.

Relevant agencies have been asked "to transport fresh water to ponds and reservoirs in the district to maintain fresh water supply to people there," the report said.

During this dry season, prolonged drought and deeper saline intrusion in the upper Tien river have surrounded communities with salty water.

The Mekong Delta faces saltwater intrusion every year, but more intense hot weather and rising sea levels -- both driven by climate change -- are increasing the risk.

Research published last month said Vietnam's Mekong delta, which provides food and livelihoods for tens of millions of people, faces nearly $3 billion a year in crop losses as more saltwater seeps into arable land.

Around 80,000 hectares of rice and fruit farms could be impacted by salinisation, according to the study from the Water Resources Science Institute under the environment ministry.

In 2016, which saw the worst drought in 100 years, 160,000 hectares of soil were impacted by salinisation.