Tauranga sailor Molly Meech and Alex Maloney enjoyed a near-flawless day in challenging conditions to extend their lead at the 49erFX world championships in Porto overnight (NZ time).

The Olympic silver medallists won three of their four races and finished second in the other to hold a four-point lead over the Danish combination of Jena Mai Hansen and Katja Salskov-Iversen.

They have now won four of their six races and, crucially, their worst result, and discard so far, is a third.

Erica Dawson and Kate Stewart also had a good day, jumping from 33rd overall to eighth on the back of a seventh and three fifth-placed finishes. They are a new combination and Stewart won a bronze with her sister Greta in the smaller 29er at the 2016 Aon Youth Sailing World Championships in Auckland.

The fog and light winds that plagued the first two-and-a-half days of the regatta in Porto were absent and replaced by large swells and a good breeze of 15-20 knots. It made boat handling challenging, particularly as the wind increased later in the day.

Molly and Alex excelled, posting four excellent scores.

"We had beautiful conditions, an increasing breeze and a nice swell to play with," says Alex. "The waves made the sailing a good challenge, particularly downwind, but it can also give you a nice ride so it was a lot of fun out there.

"We were aiming for a consistent day on the water and we managed four good races. Our goal was to keep things pretty simple. We felt fast and we were putting the boat in good positions around the race course."

The top 20 now race in gold fleet with the top 10 then qualifying for Saturday night's (NZ time) double-points medal race.

"The top boats get to race each other finally," says Alex. "After a slow start to the championship it feels like we are well under way now and we're looking forward to the next two days of racing."

Josh Porebski and Tauranga sailor Trent Rippey also qualified for gold fleet in the men's 49er but slipped down the leaderboard overnight.

The pair started the day in seventh but dropped to 14th, with a capsize on the final beat of the first race hurting their position, but they otherwise had a solid day with two top-10 results.

"It was a really challenging day out there," says Josh. "We had a regatta of no wind and now it's really windy and looking like it will stay like that for the rest of the regatta. We had huge waves and a strong wind and lots of people were capsizing.

"We're really happy to get into the top 20 so that's a positive and we'll take it race by race tomorrow."

Fellow Kiwis Hamilton sailor Isaac McHardie, who has spent a lot of time sailing in Tauranga, and William McKenzie just missed out on the top 20, ending the day in 24th on the back of an eighth, 14th and 10th.

Results and standings from the 49er world championships in Porto overnight (NZ time):

49er (81 boats)

1st: Dylan Fletcher-Scott / Stuart Bithell (GBR) 1 5 (16) 1 1 1 - 9 points

2nd: Diego Botinle Chever / Iago Lopez Marra (ESP) 1 (UFD) 2 2 3 5 - 13 pts

3rd: Justus Schmidt / Max Boehme (GER) 4 3 2 2 (6) 2 - 13 pts

14th: Josh Porebski / Trent Rippey (NZL) 8 3 4 (13) 5 10 - 30 pts

24th: Isaac McHardie / William McKenzie 8 4 11 8 (14) 10 - 41 pts

49erFX (56 boats)

1st: Alex Maloney / Molly Meech (NZL) (3) 1 1 2 1 1 - 6 points

2nd: Jena Mai Hansen / Katja Salskov-Iversen (DEN) 1 5 1 (6) 1 2 - 10 pts

3rd Martine Grael / Kahena Kunze (BRA) (6) 1 4 2 4 3 - 14 pts

8th: Erica Dawson / Kate Stewart (NZL) 4 (26) 7 5 5 5 - 26 pts