Her time smashed the World Cup championship record of 8:04.61 set by Friis in 2009 and also the Commonwealth record of England's double Olympic champion Rebecca Adlington by seven seconds.
Earlier Boyle had finished seventh in the final of the 200m freestyle in 1:55.17 after breaking her own national record in the heats. She was fifth fastest in qualifying in 1:54.97, which was nearly half a second faster than the New Zealand record she set at December's world championships in Turkey.
Boyle races in the 400m freestyle on the second day of competition, before racing in the second leg of the FINA World Cup in Berlin at the weekend.
Earlier fellow North Shore teammate Shaun Burnett was 12th fastest in heats of the 200m butterfly in a personal best 1:57.03.
Results:
Women 800m freestyle: Lauren Boyle (NZL) 8:01.22, 1 (Commonwealth & NZ Record); Mireia Belmonte Garcia (ESP) 8:01.43, 2; Lotte Friis (DEN) 8:09.84, 3. Women 200m freestyle: Sarah Sjoestroem (SWE) 1:52.26, 1; Katinka Hosszu (HUN) 1:52.32, 2; Emma McKeon (AUS) 1:53.06, 3. Also: Lauren Boyle (NZL) 1:55.17, 7.
Heats: Men 200m butterfly: Chad Le Clos (RSA) 1:52.85, 1; Thomas Shields (USA) 1:53.09, 2; Takeshi Matsuda (JPN) 1:53.42, 3. Also: Shaun Burnett (NZL) 1:57.03, 12.
Women 200m freestyle: Melanie Costa Schmid (ESP) 1:53.26, 1; Katinka Hosszu (HUN) 1:53.76, 2; Famke Heemskerk (NED) 1:53.97, 3. Also: Lauren Boyle (NZL) 1:54.97, 5 (NZ Record).