UK coastguards were told the ship was heading for Bejaia in Algeria
A search is under way for a cargo ship which may have travelled through the English Channel after apparently being hijacked by pirates.
Coastguards fear the Maltese-flagged Arctic Sea, carrying up to 15 Russian crew, was hijacked in the Baltic sea.
UK authorities had the last known contact with it as it entered the Strait of Dover. Up to five Russian navy warships are seeking the vessel.
The Maritime and Coastguard Agency said the situation was "bizarre".
Spokesman Mark Clark said: "Who would think that a hijacked ship could pass through one of the most policed and concentrated waters in the world?
"It seems strange to think that a ship which had been hijacked was passing along the channel along with ships carrying day-trippers going over to Calais."
Hijackers may have been coercing the ship's crew when they made radio contact with coastguards at Dover on 28 July, the MCA fears.
Mr Clark said the person on board whom coastguards had spoken to had told them the ship was due to arrive in Bejaia, northern Algeria, on 4 August at 2300 BST.
Reports say Swedish authorities have been told by the Finnish shipping line operating the 3,988-tonne cargo ship that on July 24 it was boarded by up to 10 armed men claiming to be anti-drugs police as it sailed through the Baltic sea.
The intruders apparently left the vessel - which was carrying about £1m worth of sawn timber from Finland to Algeria - 12 hours later on an inflatable boat after damaging the Arctic Sea's communications equipment.
BBC security correspondent Frank Gardner said many questions remained unanswered.
He said: "If masked men took over the ship off the coast of Sweden, which in itself if pretty staggering... then made off by speedboat... why didn't the crew report all of this immediately and where are they now?
"The worrying thing is that this happened right off the British coast. Piracy in this country is unheard of, not since the days of Cornish brigands a long, long time ago."
On 3 August, Interpol told Dover Coastguard the crew had been hijacked in the Baltic Sea and asked UK authorities to be alert as the vessel passed through the channel.
But by then the ship had already left the Strait of Dover, having last been recorded off the coast of Brest, northern France, just before 0130 BST on 30 July.
The MCA said it was told the vessel had seemingly been spotted by a Portuguese coastal patrol aircraft but its current location was unknown.
Mr Clark said nothing seemed suspicious when the ship made contact, adding: "It could well be that a crew member had a gun put to his head by a hijacker when contact was made, but who knows?"
Two nuclear submarines are among the five Russian navy vessels searching for the ship, according to Moscow's Itar-Tass news agency.
Commander-in-chief Vladimir Vysotsky told the agency: "On orders from President Dmitry Medvedev, all ships and vessels of the Russian Navy in the Atlantic have been dispatched to search for the missing ship."
Naval staff had no indication of the ship's location, despite reports it may be off West Africa, he added.
Mark Dickinson, general secretary of seafarers' union Nautilus International, said the situation was "unbelievable" and criticised authorities for their "relaxed" view of marine hijacking, in comparison with that of aircraft.
"It is alarming that, in the 21st Century, a ship can apparently be commandeered by hijackers and sail through the world's busiest waterway with no alarm being raised and no naval vessel going to intercept it," he said.
World leaders have become increasingly concerned about pirates operating off the coast of Somalia.
But Nick Davis, who runs the private security firm Anti-Piracy Maritime Security Solutions, told the BBC's Today programme the relatively low value of the cargo suggested this was a different kind of piracy to that seen off the coast of East Africa.
Instead, he suggested, it was more likely that the apparent seizure was the result of a "commercial dispute" in which one party had decided to "take matters into their own hands".
He added: "Piracy is piracy - if someone's wanting to take that vessel, and they're not authorised, and they use a speedboat to go and get it, then it's no different to what the Somalis do.
"However, I don't believe they would have boarded that vessel firing weapons in the air, and threatening to kill the crew."