Anti-hunting campaigners have called on the public to inform police of illegal hunts, after a ban on the activity came into force in England and Wales.
Hunts must now follow a number of alternatives to hunting with hounds
"These are crimes, criminal events, and that is for the police to deal with," said the head of the League Against Cruel Sports, Douglas Batchelor.
The league plans to train hunt monitors to provide evidence for prosecutions.
The Countryside Alliance said many hunts will held - within the limits of the new law - this weekend.
The Association of Chief Police Officers spokesman, Nigel Yeo, said he expected most people would obey the law - by drag hunting or chasing foxes then shooting them.
He said police would challenge any hunts which are threatening to break the law.
The League Against Cruel Sports launched its Hunt Crime Watch programme to observe hunts and to provide police with evidence which can be used in prosecutions.
But Mr Batchelor said people who had seen illegal hunting practices may be reluctant to report them to the authorities.
"Over the years we've had a lot of contacts with people who have been concerned about the level of intimidation and violence that's been associated with some of the hunting fraternity.
"If people are not prepared to go to the police then of course they should come to us and we will maintain their anonymity."
WAYS TO HUNT LEGALLY
Hunting rabbits or rats instead of foxes or hares
Using no more than two dogs to flush out a fox to be shot
Drag or trail hunting (using an artificial scent to hunt with hounds)
Using hounds to flush out a mammal to be hunted by a bird of prey
Exercising packs of hounds without using them to hunt
Using terriers to flush and shoot foxes, to protect gamebirds
The Attorney General, Lord Goldsmith, has so far issued no instructions to police on how they should deal with hunters who violate the law.
He said he will consult the Director of Public Prosecutions and the police "in the near future" to decide what measures to take with regards to hunting prosecutions.
He has rejected a "blanket policy" of not enforcing the ban until the House of Lords has considered its legality.
Simon Hart of the Countryside Alliance has questioned how police will ensure there are no violations of the new laws.
"The definitions of legal and illegal hunting are so blurred that the police are being asked to make impossible judgements.
"You can hunt a rat, but not a mouse, a rabbit but not a hare, an artificial scent, but not a real one," he said.
'Hunting will return'
The Beaufort Hunt had one pack out on Thursday and has promised a hunt this weekend.
Under the new law hunters have a number of legal options available to them.
As well as being able to mount a hunt for an artificial scent, it will still be legal for the hunts to "flush out" foxes, as long as they shoot their quarry rather than set the hounds on them.
"We are not going away. We will keep these hounds going, we will keep this community going and in the end we will come back and hunt when hunting is legal again," said hunt master Captain Ian Farquhar.
But Tony Banks, Labour MP for West Ham, said the issue would soon disappear, and that "people in a few years time will be wondering what it was all about".
He said had the government not prevaricated since 1997 in introducing the ban, hunting with dogs would have passed into history like other former country pursuits such as otter hunting and badger baiting.
"Let the election decide this because the Conservatives have made clear that if they get elected into government they will restore hunting," he said.