GENEVA (AFP) - The conflict in Ukraine has driven more than 824,000 people from their homes, but the real number could be far higher, the United Nations said on Friday, as it scrambled aid to offset the impact of winter.

At least 430,000 people had been displaced within Ukraine as of Thursday, according to the UNHCR refugee agency, up 170,000 since early September.

"With the crisis in Ukraine entering its first winter, UNHCR is racing to help some of the most vulnerable displaced people cope with expected harsh winter conditions," UNHRC spokesman Adrian Edwards told reporters.

But he said the real picture is still emerging. "Ongoing fighting in the east, and the resulting breakdown of basic services, continues to drive more people from their homes," Mr Edwards said.

Most are living in rented accommodation or staying with family or friends, but up to 18,700 are in improvised shelters which need weather-proofing, Mr Edwards said.

Ukrainian government troops have been battling pro-Russian separatists since they rose up in April, after mass protests in the ex-Soviet republic ousted Moscow-friendly president Viktor Yanukovych.

More than 3,700 people have been killed since April, according to UN figures.

In addition to people displaced within Ukraine, another 387,000 have fled to Russia, Mr Edwards said, citing official figures from Moscow.

The actual number in Russia may be far higher, given that Ukrainians do not need visas to travel there, Mr Edwards said.

Many Ukrainians have also headed westwards, either to the European Union or former Soviet republics such as Belarus.

In addition, an estimated 17,000 people have fled Crimea, the strategic Black Sea peninsula mainly populated by Russian-speakers which was annexed by Moscow in March.