Drought-stricken Swaziland Thursday said it would begin sever water rationing in the capital Mbabane after levels in the main dam supplying the city fell to a critical low.

Swaziland Water Services Corporation (SWSC) said the restrictions would begin on Friday and probably last until the arrival of summer rains expected around October.

Under the measure, there will be no mains water for four days a week. Residents will collect water from mobile tanks instead.

"This is because of the dire drought situation which has decreased water levels at the Hawane Dam," said SWSC spokeswoman Nomahlubi Matiwane.

She said water levels in the dam had dropped from 15 percent of capacity in the last few weeks to just nine percent.

Swaziland is one of a number of countries in southern Africa that have been badly hit by El Nino -- a weather phenomenon that is centered on the countries in the Pacific but can affect other regions as well.

In February, dry conditions gripping the agricultural sector prompted the government to declare a state of emergency.

Water resources in the impoverished country of 1.2 million people have more than halved, contributing to higher food prices and poor crops.

Last month aid organisations estimated that El Nino had affected 12.3 million people across southern Africa.