Canadian coastguards were last night battling to rescue hundreds of seal hunters trapped in thick ice off the country's Newfoundland east coast. Some 100 sealing vessels became stuck in drifting pack ice on Wednesday and the crews of at least four boats have already been flown to safety.

An ice-breaking coastguard ship sent to the area has also become stuck in the worst ice conditions seen in the region for 15 years, Canadian officials said.

Another five rescue boats are smashing their way through ice more than a metre thick to reach the stricken vessels. But not all of the sealers are expected to be freed before the weekend. Three coastguard helicopters are dropping food and supplies, and are on standby to evacuate more hunters if conditions worsen. About 15 vessels are in danger of ice piercing their hulls.

The Newfoundland phase of Canada's controversial seal hunt is the third and largest, in which 270,000 animals are killed for pelts and blubber.

Brian Penney, a superintendent with the coastguard in Newfoundland and Labrador, said: "There are vessels disabled, there are vessels damaged. There are crews that are out on the ice because there's quite a possibility that their vessels may sink or the vessels are out on their sides."

The coastguard is trying to get supplies to those vessels that are in the most dire straits, he said. "Supplies are starting to run very low, in addition to fuel," he added.

Many sealer crews are reluctant to abandon their vessels. In some cases boats could be crushed by the thick ice and their hulls cracked open.

Reduced ice conditions further to the south meant this year's total seal quota had been cut back from the 335,000 hunted last year. The seals use the normally widespread ice floes in the Gulf of St Lawrence and in the Atlantic Ocean to give birth to their young.

"Conditions have deteriorated over the last few days as a result of the wind pressing the ice floes into the land," a Canadian coastguard, Windross Banton, told CBC television from an icebreaker.

"There's quite a few different pockets of vessels all about the area ... unfortunately the weather conditions forecast right up until the end of this week are probably going to cause conditions to even deteriorate more so than they are now."

The hunters earn about £39 for each seal pelt - most of them destined for the fashion industry in Norway, Russia and China. But seal blubber is also sold to produce oil.

The hunt has been condemned as cruel and unnecessary by campaigners and high-profile figures including Paul McCartney. The United States has banned Canadian seal products since 1972 and the European Union banned the white pelts of baby seals in 1983.

Canada's Fisheries and Oceans Department said about two-thirds of this year's quota had already been filled.