After the Government’s Homes for Ukraine scheme opened at the weekend, Mr Javid said those arriving in the UK would get all the support they needed.
His assurance came as the latest intelligence assessment by the UK Ministry of Defence (MoD) warned that Russian forces were seeking to encircle the capital, Kyiv.
Mr Javid defended comments by Home Secretary Priti Patel who insisted security checks were needed on refugees from the war to prevent Russian spies infiltrating the country.
Speaking at the Conservative Spring Forum in Blackpool at the weekend, Ms Patel said it was “naive” to assume that just because most people arriving in the UK were women and children there could not be Kremlin agents among them.
Mr Javid said that while any checks should be “proportionate” the Salisbury nerve agent attack in 2018 underlined the need to be vigilant.
“We saw in our country Russian agents came here with a deadly nerve agent, a chemical weapon, and they used it in Salisbury. We know it killed people and Russia was directly responsible for that,” he told Sky News.
“They infiltrated our country with agents, with a chemical weapon, and used it and so it is right there are some level of security checks. We also know that extremists and extremist organisations operate in that region.”
Mr Javid said the UK had already issued 9,500 visas to Ukrainians with family ties to the UK, while 150,000 people had expressed in an interested in hosting refugees through the Homes for Ukraine programme.
“I’m pleased that we are supporting Ukraine in every single way that we can, whether that’s military aid, humanitarian aid, or indeed providing sanctuary for those that are fleeing Ukraine,” he told LBC.
“I expect that we will see hundreds of thousands of Ukrainians arrive here in the UK, and they will get all the support that they need.”
According to the latest MoD assessment, the Russian advance on Kyiv remains stalled in the face of determined Ukrainian resistance with the bulk of Moscow’s forces still more than 25km (15 miles) from the centre.
Nevertheless, analysts believe the capital is still the Kremlin’s main military objective although it is thought the Russians will try to force it into submission through encirclement rather than attempting a direct assault.
“Forces advancing from the direction of Hostomel to the north-west have been repulsed by fierce Ukrainian resistance,” the MoD said.
“Despite the continued lack of progress, Kyiv remains Russia’s primary military objective and they are likely to prioritise attempting to encircle the city over the coming weeks.”
President Joe Biden will hold a conference call with key European leaders – including Boris Johnson – to discuss the latest situation in Ukraine ahead of a Nato summit in Brussels on Thursday.
Earlier Foreign Secretary Liz Truss condemned the reported enforced deportation of civilians from the besieged city of Mariupol for transportation to Russia.
On Sunday, the Russians said residents would be allowed to leave the city, which has largely been reduced to rubble by weeks of heavy fighting, if the defenders laid down their arms.
The offer was swiftly rejected by the Ukrainian authorities amid deep distrust over Russian intentions.
Over the weekend, the city authorities said a bomb destroyed an art school where 400 people had taken shelter, with rescuers searching for people possibly trapped under the rubble.
Only days before the shelling, there was a separate attack on a theatre in the city where more than 1,000 people were said to have been seeking shelter.
Ms Truss tweeted: “I am appalled by Russian atrocities in Mariupol, including attacks on schools sheltering civilians and the abduction and deportation of Ukrainians.
“Putin is resorting to desperate measures as he is not achieving his objectives. Putin and his regime will be held to account.”