Tokyo was bracing for a night of macabre revelry on Saturday as party-goers flocked to buy wacky costumes for the evening's Halloween celebrations.

For the normally reserved Japanese, Halloween is an excuse to let their hair down as they dress up as blood-spattered ghouls, fluffy animal characters or foxy nurses at pumpkin-decorated parties across the country.

"I will put a spell on you," nine-year-old Yuta Shimizu warned AFP, waving a wand as his Harry Potter spectacles slipped down his nose. "I can turn you into a lizard."

Pint-sized friends of Shimizu trick-or-treating their way around Tokyo's hipster neighbourhood of Shimokitazawa included a pirate, a firefighter and a petite Maleficent.

Halloween is a billion-dollar industry in Japan, enjoyed by an estimated 20 million people across the country, and where shops are decked out with pumpkins and jack-o'-lanterns while eateries and convenience stories offer pumpkin-flavoured drinks and desserts.

Parades last weekend staged in Tokyo's Roppongi district and in Kawasaki, south of the capital, drew 100,000 spectators each, according to organisers.

"This is poison," said 29-year-old Aki Nakano, done up as a zombie nurse and brandishing a syringe filled with a blood-red alcohol concoction she was squirting into the mouths of club-goers earlier this week for 500 yen ($4) a shot.

"Halloween is my favourite time of year," she added. "I work in an office and I don't get a chance any other time of the year to dress however I want -- a bit, sort of, slutty."

Train carriages were already filling up with party-goers from late afternoon with one foreigner dressed as cult mascot hero "Funassyi" and leaping up and down with a high-pitched squeal as the squidgy funster himself.

"Imagine trying to do this in the States," said the American, invisible under his yellow mask and declining to give his name. "We'll keep riding the train until it gets dark and then go to a club."

Police at the iconic "scramble" crossroads in trendy Shibuya were bracing themselves for a long night, meanwhile, as Tokyo Disneyland was preparing for a record weekend.

Halloween events were also being planned across Japan -- from icy Sapporo in the far north to the honeymoon isles of Okinawa in the south of the country.

"I've dressed as a vampire to go with my Transylvanian roots," said Romanian-born DJ and event organiser Dani Savant, on his way to spin at the 'Scream' Halloween party in Shibuya. "Halloween gives Japanese the opportunity to come out of their shell and go crazy. It's so awesome to see!"