Swimmer Neil Agius has battled strong currents and an ankle injury overnight as he attempts to set a world record for the longest open water swim.

The 35-year-old began his non-stop journey on Monday evening from Linosa, an Italian island north of Lampedusa, to Malta.

He hopes to set the world record for the longest continuous, unassisted, current-neutral swim along a single-segment natural route in an ocean, sea or bay, which is currently set at 124.4km.

In an update at 8am on Tuesday, his team said Agius had spent a "very tough night" at sea.

"There is a strong north current working against Neil and the waves were constantly hitting him from the front and side. The weather remains variable," they said.

"The pace was slow throughout the night and he had a sharp pain in his left ankle. This is the reality of an expedition that has never been completed before."

As of 8am, Agius had swum a total of 30km in 14.5 hours, leaving him a quarter way through his challenge.

Neil's attempt to complete the 130 kilometres distance began with a marriage proposal on Monday from his long-term girlfriend Lara Vella. The swim is expected to take 50 to 55 hours. 

Neil Agius and fiancee Lara Vella embrace after they got engaged, shortly before the world record swim attempt. Photo: Kurt Arrigo/Neil Agius

In its Facebook post, Agius' team said he was in excellent spirits, covering the first 10km in less than two hours.

Following a tough night, his pace was again picking up on Tuesday morning. Readers can follow the swim, live on the Wave of Change race tracker. 

Agius is swimming to raise awareness of plastic waste in the sea and is asking people to support him by getting involved in the 'Double the Wave' challenge.

Neil Agius in a previous swim. Photo: Matthew Mirabelli

This can be done by:

• picking up six pieces of plastic;
• posting a video of yourself on social media doing six repetitions of your favourite exercise with the pieces of plastic in the video;
• Use #doublethewave and tag Wave Of Change Malta;
• Tag and nominate six people.

Agius has originally planned to swim from Tunisia to Sicily but plans had to be changed. 

On Thursday, he warned that bad weather in Tunisia would not allow the ideal conditions for the swim to take place, and while it was a “tough pill to swallow”, the navigation team had been looking into alternate routes for the swim to take place regardless.