The Prime Minister has recalled her cabinet ministers from an Easter break in anticipation of action, and they will be asked to "consider the next steps" at a meeting this afternoon, a Downing Street source told The Times.
Britain would work with United States and France to coordinate an worldwide response, the statement said.
US President Donald Trump warned Russian Federation yesterday of imminent military action in Syria, declaring that missiles "will be coming" and lambasting Moscow for standing by Syrian President Bashar al-Assad.
Some MPs have backed Britain acting against Syria, warning that the use of chemical weapons was in breach of worldwide law and could not be allowed to go unpunished.
Sky News reported that May is expected to ask the ministers to greenlight the UK's participation in an attack spearheaded by France and the U.S., without consulting the Parliament.
Britain's government weighed the possibility of military action against Syria on Thursday but faced growing scepticism from opposition leaders and deeper divisions in a country still haunted by its role in the US-led invasion of Iraq.
The No 10 statement issued following the Cabinet meeting said Mrs May had again described the attack on Douma as a "shocking and barbaric act" which represented a further erosion of worldwide law.
May, also speaking earlier on Wednesday, said all the indications were that the Syrian authorities were responsible for the chemical attack in the town of Douma and that such shocking assaults could not go unchallenged.
Donald Trump has also threatened military action.
Mr Trump provided a fresh twist on the escalating global crisis yesterday, issuing a fresh tweet saying: "Never said when an attack on Syria would take place".
Which is why the Syrian crisis, and the whole debate over Britain's participation in military action against the Assad regime, has forced Mrs May out of her political comfort zone and compelled her, for once, to provide some decisive leadership. "Could be very soon or not so soon at all!" he tweeted, without ruling out attacks.
British Prime Minister Theresa May has ordered United Kingdom submarines to move within missile range of Syria. Get ready Russian Federation, because they will be coming, nice and new and "smart!"
The newspaper said it had learnt that the prime minister had ordered submarines to get within missile range to Syria.
"Parliament should always be given a say on any military action", opposition Labour leader Jeremy Corbyn told the BBC.
"The use of chemical weapons can not go unchallenged..." May is not required by law to consult the House of Commons, but by convention, members of Parliament expect to be consulted.
Meanwhile, Brexit minister David Davis said Britain has not yet decided on precisely how to respond to the chemical attack, claiming any move would be carefully considered by the government. We can not risk an escalation even further than it's gone'.
Some lawmakers have expressed reservations about taking military action now, but others have come to believe the 2013 vote was a mistake.
But the Syrian chemical weapons attack means that, on this occasion, she has nowhere to hide.