Nearly half of those people (44 percent) were considering further relocation due to the scale of the humanitarian crisis in the country, a survey by the International Organisation for Migration (IOM) found.
The figure is up from the estimate of 7.7 million that the IOM gave on April 17.
Indiscriminate bombing campaigns by Vladimir Putin’s forces have laid waste to major Ukrainian cities and are believed to have caused thousands of civilian casualties.
Around 5.9 million people have already fled the country since the invasion.
“The needs of those internally displaced and all affected by the war in Ukraine are growing by the hour,” said IOM director general Antonio Vitorino.
“Access to populations in need of aid remains a challenge amid active hostilities, but our teams are committed to continue delivering urgent assistance inside Ukraine and in neighbouring countries.”
The IOM’s survey was conducted between April 29 and May 3.
Nearly two-thirds (63 per cent) of internally displaced people are estimated to be women, the IOM said.
Around half have fled from the eastern region of Ukraine where Russia has ramped up its military activity after failing to take Kyiv and other central Ukrainian cities.
“Nine percent of all people surveyed in the latest report, including those not internally displaced, indicated that their homes were damaged or destroyed,” the IOM said.
“Among the internally displaced alone, this figure rose to 27 percent. Every one out of 10 people surveyed said that they would need materials to fix damaged homes.”
In other developments, the Ukrainian military said Tuesday that Mr Putin’s forces were continuing to pound the southern port city of Odessa with rockets as part of efforts to disrupt supply lines.
One person was killed and five were wounded after Russian forces struck a shopping centre and a warehouse, the military said.
In Mariupol, Russians also bombarded the Azovstal steel mill, the Azov regiment said.