It's 4 am and Tsukiji fish market is humming with activity. Workers shout and shuffle styrofoam boxes of fish, and dodge nimbly as electric scooter trucks whiz past. Wholesalers take orders and man their stalls, which stretch for several city blocks through the mist rising off the ice.

This is a daily scene here in the biggest fish market in the world. Tsukiji, officially known as Tokyo Central Wholesale Market, moves 2,000 tons of fish and seafood a day, plus tons of flowers, fruit, vegetables, meat and sundry other things as well. It is also one of Tokyo's most interesting and unusual tourist attractions, luring people from all over the world to watch the action. And since the action mostly takes place in the wee hours of the morning, it's a good destination for jet-lagged travelers -- a few bleary-eyed groups could be seen here and there taking pictures and peering into boxes of slimy sea creatures.

It can be a bit overwhelming at first for newcomers. My companion, who was visiting for the first time, after a few minutes gazing about with a dazed expression, started muttering darkly about overfishing and why we should all be vegetarians.

As 5:30 rolls around, the tuna auction begins. The frozen tuna carcasses, caked in frost and minus their tails, are lined up in neat rows each with a fan-shaped slice near where the tail had been, pulled up to allow inspection of the meat by prospective buyers. The auctioneer, his face animated as he takes the bids, keeps the patter coming in a continuous stream of sound as he auctions off the night's shipment of frozen tuna. The audience of a few dozen wholesalers and jobbers, all registered bidders, know what they're doing -- the whole shipment is sold in a few minutes. They bid, barely raising their cards, the auction is quickly over and the crowd disperses. Workers descend on the frozen tuna carcasses, paint their new owner's name on them and lug them to the wholesalers' stalls where they're cut up into saleable-size chunks.

The frozen tuna are sliced into pieces like logs using bandsaws, while fresh fish are cut with knives called "oroshi hocho" (literally: "wholesale knife"), a meter-long sword-looking thing specially designed for cutting up tuna and other large fish. The blade is 150cm long and can fillet a big tuna in a single cut, usually with two or three people working together to handle the knife and the fish. Other workers hack away at frozen tuna chunks with axes, circular saws and hand saws.

Actually, Tsukiji is only one of 10 wholesale markets in Tokyo, but it is by far the biggest, and the best known. It traces its history back 400 years, to the days of the Tokugawa shogunate, when Tokugawa Ieyasu granted permission to a group of fishermen to set up a market by Nihombashi bridge to supply his castle in Edo (now Tokyo). Vegetable and fruit markets sprang up at the same time. The current market was established in 1935.

There are plans afoot to build a new market equipped with computerized bidding, and close down the current facility. No doubt it will make the fish market much more efficient, but it will inevitably lose a large measure of the excitement, as well as the sights and smells of the old market in full swing.

By 8:00 the action is winding down, and so are we. My companion, having gotten over her vegetarianism, agrees to stop in at a little sushi shop in the outer market for a sushi breakfast.

The outer market is starting to bustle as stall owners set up their displays -- handmade knives, sweets, "kamaboko" (processed fish paste), cooked whole octopus, various kinds of fish guts, tuna heads, rice crackers, cooked fish, raw fish, kitchen goods, and every sea creature known to man. The restaurant, not much larger than a stall, is packed with tired workers smoking and drinking beer as they come off shift. The maguro and kampachi we're eating is succulent and full of flavor, probably the best we've ever eaten. Sashimi doesn't get any fresher than this.