Mounties have boarded a cargo ship off British Columbia carrying hundreds of migrants believed to be Tamils from Sri Lanka and are escorting it to Vancouver Island.

The RCMP say their officers boarded the MV Sun Sea shortly after 6 p.m. when it entered Canadian territorial waters. The ship was then being brought into port at CFB Esquimalt.

The migrants may include dozens of children, says a lawyer who has heard from the migrants' families.

"There's a large number of children, children under 13," said Lorne Waldman, who represented many of the Sri Lankan migrants that arrived in a similar way last October.

Public Safety Minister Vic Toews originally said the navy had boarded the ship, but government officials corrected the record later Thursday to say the ship was being escorted and would be boarded later.

Toews labelled some of the 490 passengers on the ship "human smugglers and terrorists," although he didn't elaborate. He used the ship's arrival to promise swift action from Ottawa.

"Human smugglers and human traffickers are now watching Canada's response to judge whether or not they can continue to take advantage of us," he said.

Toews said the government will be sending a message "loud and clear" that human smugglers will be prosecuted, though he provided no details.

Transport Canada confirmed Thursday the ship will be taken to Esquimalt harbour at CFB Esquimalt and that air traffic will be restricted from above the vessel as it travels and while it is docked.

A crew member on a neighbouring fishing vessel had been listening in on radio transmissions and told The Canadian Press the people on the MV Sun Sea were peppered with questions from the coast guard.

"Just asking 10,000 questions, about how many sick, how many dead, how many women, how many children -- many, many, many questions," Rory Smith, the chief mate on a fishing vessel that was positioned several kilometres from the ship early Thursday afternoon, said in an interview over satellite phone.

"It was 490 people on board, then it was 480, then it was 450. No dead, they had one that was probably sick," he said, recalling the answers to those questions.

There have been reports that one person aboard the cargo ship is dead.

Smith said the ship in communication with the coast guard shows up on his vessel's navigation equipment as the MV Harin Panich 19, which is the name of the ship before it became known as the MV Sun Sea.

The fisherman said the ship's crew indicated they are from Sri Lanka and eager to reach Canadian shores

"They're very happy to be here, they've suffered all their lives and they're very happy to be in Canada," said Smith.

"I'm from Florida, so this is a daily thing down there," Smith added, pointing to the flow of migrants from Cuba and Haiti.

Smith said his radar indicated the ship was being escorted by navy vessels, although he couldn't see the Sun Sea through thick fog.

Last October, 76 Tamil migrants arrived on a ship boarded by Canadian authorities and there were similar concerns there may be members of the Tamil Tigers, a banned terrorist organization.

All of the men were immediately detained in jails around the Vancouver area, but most were let go within weeks. Months later, only one remained in custody on suspicion of being a Tiger.

By this past spring, he, too, had been released.

Waldman said members of the large Tamil community in Toronto have been contacted by relatives on the boat in recent days.

In turn, family in Canada have called Waldman's office looking for advice.

"Apparently there are some people that are quite ill on the boat. And I gather the authorities are now aware of that and are making arrangements to meet them," Waldman said.

"I know that there's already preparations for the children to be taken to a special sick tent."

Detention reviews for the migrants are expected to begin Monday, said Waldman, who represents about 30 of the migrants who turned up on the Ocean Lady last year.

Waldman said his office is working with people in B.C. to ensure the migrants have swift access to legal counsel, as many who arrived on the Ocean Lady did not have ready advice.

"The whole experience was very intimidating and bewildering for them because they didn't understand what the process was."

Reader comments on news sites suggested many Canadians believe the Canadian government should simply have turned the MV Sun Sea around.

But Toews said "the best legal case for prosecuting criminals responsible for illegal acts of this nature at this time is to intercept them in Canadian waters, rather than on the high seas."

As a signatory to the UN Convention on Refugees, Canada must process all refugee claimants who manage to reach Canadian soil

The ship was expected to sail through the Juan de Fuca Strait before landing in the Victoria region, and preparations appeared underway at nearby Canadian Forces Base Esquimalt and at a nearby naval refuelling station, where massive tents had been erected.

Two Vancouver-area jails have been told to make room for a flood of new inmates this week and a news helicopter has broadcast footage of tents and portable toilets set up at CFB Esquimalt.

A local hospital had set aside a special area for any passengers requiring medical attention.