Up to one million people face water shortages in eastern Ukraine as workers battle to repair pipes damaged by fighting in rebel-held Donetsk, a city spokesman said on Thursday.

"Today the water supply is limited and a full supply is being provided only at certain times," Maxim Rovinsky, spokesman for Donetsk mayor Oleksandr Lukyanchenko, told AFP.

The city is the largest rebel stronghold in eastern Ukraine and the epicentre of the self-proclaimed Donetsk People's Republic.

Rovinsky said water would reach residents in five-hour stretches every morning and evening, in restrictions that went into force on Tuesday.

The region is suffering from severe water shortages after weeks of fierce fighting between pro-Russian rebels and Ukrainian troops damaged vital infrastructure.

There has been no water supply to the battle-ravaged northern city of Slavyansk -- which has a population of 120,000 -- since the start of the month. Many other towns have had their supply restricted.

"As of today the water supply to Donetsk is down 20 percent," Rovinsky said.

The city has been unable to access a canal -- its main water source -- since a June 10 artillery attack on a pumping station that killed two workers and seriously damaged pipelines.

Rovinsky said engineers were initially unable to access the pumping station due to ongoing fighting, but had begun repair work following mediation between separatist fighters and Ukrainian forces.

"We hope that today or tomorrow they will finish repairs and the water supply will be fully restored," Rovinsky said.

Administrative control of Donetsk is split between officials loyal to Kiev and pro-Russian militants, who this week stormed the city's central bank.

Donetsk's pro-Kiev authorities, which now operate out of temporary offices after rebels stormed their headquarters, warned on Wednesday that water was running low in several towns across eastern Ukraine.