An offence is to be created to stop paedophiles soliciting explicit photos from children online or via mobiles.
Intelligence experts and organised crime specialists will join forces to tackle child abuse images on the "dark net", David Cameron has said.
It is illegal in England and Wales to possess such images but not to ask a child to send them. David Cameron will say there can be no "grey areas".
The prime minister said a joint GCHQ and National Crime Agency unit would hunt online paedophiles with the same "effort" used to track terrorists.
In a speech later, the prime minister will say he is determined to stop adults "grooming" children online.
Speaking at a London summit, he said online child exploitation existed on an "almost industrial scale" worldwide.
He has also announced a new unit, including GCHQ intelligence experts, to tackle abuse images on the "dark net".
He also unveiled a law to stop adults sending children "sexual" messages.
The joint GCHQ and National Crime Agency unit will use "every bit of effort" used in hunting "terrorists and other international criminals" to pursue paedophiles who share abuse images, Mr Cameron said.
Mr Cameron said the new unit was part of a drive to remove millions of "sickening and depraved" images from the internet.
'Alarming phenomenon'
The term "dark net" refers to parts of the internet that are hidden and can be hard to access without special software, and Downing Street said the new unit would be able to analyse huge volumes of child abuse images.
The new offence of sexual communication with a child will be punishable by up to two years in prison.
Mr Cameron said progress had been made on blocking online abuse images, but added: "The dark net is the next side of the problem, where paedophiles and perverts are sharing images, not using the normal parts of the internet that we all use.
Mr Cameron is expected to give more details when he speaks at the We Protect Children Online summit in London later.
"What we are doing there is setting GCHQ, our world class intelligence agency, together with the National Crime Agency and we are going to go after these people with every bit of effort that we go after terrorists and other international criminals."
He is expected to say: "We have seen an increasing and alarming phenomenon of adults grooming children online, encouraging them to send images of themselves over the internet or on mobile phones.
No 'grey areas'
"There can be no grey areas here. If you ask a child to take their clothes off and send a picture, you are as guilty as if you did that in person.
Mr Cameron, who is speaking at the We Protect Children Online summit in London, said his proposed new law would make it "illegal for an adult to send a sexual communication to a child".
"So we are changing the law. Just as it is illegal to produce and possess images of child abuse... now we are making it illegal to solicit these images too."
The law, which would apply in England and Wales, is expected to be included in the Serious Crime Bill currently going through Parliament.
Mr Cameron will use the summit, attended by internet firms and experts, to announce that the Serious Crime Bill currently going through Parliament will be used to introduce the new measures.
Various laws exist in this area, but Mr Cameron said there should be no "grey areas".
It will also be made illegal to possess material offering guidance on abusing children.
He said it would also be made illegal to possess material offering guidance on abusing children - what he called "paedophile training manuals".
It is already against the law for an adult to exchange explicit images by text or via the internet with someone under the age of 16 but there is no specific law preventing them from requesting sexual pictures.
Although prosecutors have attempted to use other legislation, such as the Sexual Offences Act 2003, to pursue online paedophiles grooming children in this way, they have had to prove that incitement to commit sexual activity took place.
The new offence will make it illegal for anyone over 18 to talk about sex to a child under the age of 16 on a chat room, send sexually explicit text messages or invite them to communicate sexually.
It follows a campaign by the NSPCC charity to close what it dubbed the "flaw in the law".
'Digital fingerprints'
The summit will also hear of new solutions developed by tech giants including Microsoft, Google, Facebook and Twitter to track down offenders.
"Digital fingerprints" of thousands of known child sex abuse photographs identified by UK charity the Internet Watch Foundation will be used to block images being shared.
Mr Cameron will announce that technology identifying and blocking known child abuse videos has been developed by Google and will be rolled out to the wider industry.
It is also understood that Microsoft, Google and Mozilla are to look into building restrictions into their browsers - Internet Explorer, Chrome and Firefox - to prevent people accessing the websites of known child abuse material.
Mr Cameron said: "Every time someone chooses to view an online image or a video of a child being abused, they are choosing to participate in a horrific crime.
"I want to build a better future for our children. The package I am announcing today is a watershed moment in reducing the volume of child abuse images online."
Representatives from more than 50 countries, 23 leading technology companies and nine non-governmental organisations are attending We Protect Children Online summit.
A series of commitments from more than 30 countries to increase law enforcement in the field will also be unveiled.
