A rider has been airlifted to hospital after a crash in the final lap of the practice session.
The European rider, who was riding a Superstock machine, crashed at Primrose corner, close to the start/finish area of the circuit just four minutes before the session was due to end.
No other bikes were involved.
The rider received lengthy treatment at the scene before being taken by helicopter to hospital in Belfast.
It is not known at this stage if his injuries are life threatening.
Post update
RED FLAG
The red flag is out and, with roads opening again soon, the session is over.
Austrian peaks in Superstock
Horst Saiger from Austria is the surprise name at the top of the Superstock practice times with Michael Rutter second and Stephen Thompson third.
Breaking the limit
Stephen Henderson on Twitter: "Now getting messages from my mobile phone operator that I'm over my data limit. Well worth it. Great coverage.
Amor loving the North West
Keith Amor, a Superstock winner here four years ago, tops the Supertwin times, Ryan Farquhar is second best with Connor Behan third.
Supertwins latest
Falkirk flyer Keith Amor is leading the Supertwins with Ryan Farquhar currently second and Connor Behan third.
Supertwins ready to go
Next up are the Supertwin machines, a class introduced to the North West in 2012. They are four-stroke twin cylinder bikes originally sold for road use with a water cooled engine of up to 650cc.
Superbike sessions ends
Superbike placings: 1) Michael Rutter; 2) Alastair Seeley; 3) Guy Martin; 4) William Dunlop; 5) Martin Jessopp; 6) Josh Brooks
Superbike session
Latest is that Alastair Seeley is setting the Superbike pace, closely followed by Guy Martin, William Dunlop, Michael Rutter and Michael Dunlop.
Pace notes
Marty Tweets from University: "Sitting at my desk in Cambridge watching online trying to look like I'm working hard. If they only knew. Flying over tomorrow so happy days."
Post update
PAcemakerCopyright: PAcemaker
Ian Hutchinson comes off his Milwaukee Yamaha during the first Supersport practice session on TuesdayImage caption: Ian Hutchinson comes off his Milwaukee Yamaha during the first Supersport practice session on Tuesday
Ian Hutchinson has gone to hospital for a check-up after coming off on the Mill Road section during the Supersport session.
Supersport session ends
William Dunlop tops the unofficial time sheets in the Supersport, Michael Rutter second and Alastair Seeley third.
"I always liked the wee 600 - the bike has been working really well," says Dunlop.
W Dunlop 114.754; Rutter 114.192; Seeley 114.179; L Johnston 114.118; G Johnson 113.828.
Press EyeCopyright: Press Eye
William Dunlop was fastest in the first Supersport practiceImage caption: William Dunlop was fastest in the first Supersport practice
Post update
Steve Parrish
BBC motorcycling commentator
Josh Brookes will be happy. I think he's got more laps in already then he managed in all of last year's North West.
Seeley stops
Setback for Alastair Seeley: "We have had to pull in with a bit of an engine problem which is a bit disheartening. I'll have to speak with the boys and see what the problem is."
Update on timings
William Dunlop setting pace
From @northwest200: 15 mins gone of a 35 min session and it is William Dunlop 113.568 ahead of Seeley 112.290 Johnson 112.331 Martin 111.785.
PIT STOP
Rutter has problems
Michael Rutter is back in the pits hoping mechanics can sort out an early problem with his Smiths Triumph machine. "We have one or two things to do, hopefully we can get a few laps in," says the 13-times North West winner.
Post update
Weather watching
A Tweet from the Thruxtonian: The weather is better at your end than here in Barcelona. It's not fair!
Starting soon
The Supersports are on the grid for the first 35-minute practice session
Action delayed
Stephen Watson
BBC Sport NI
Newcomers practice delayed slightly so we are now on air with live NW200 practice at 10.30
Weather outlook
Promising news from @angie_weather on Radio Ulster: "Many places having a better day today, mainly dry and bright with a light on-shore breeze on the north coast."
Tuesday's practice session
Live video streaming of the first practice session for the 2014 North West 200 starts here at 10:15 BST. The Supersport 600 machines will be getting their first run on the 8.9-mile Triangle circuit at 10:30.
Live Reporting
Lyle Jackson
All times stated are UK
Get involved
PAcemakerCopyright: PAcemaker Ian Hutchinson comes off his Milwaukee Yamaha during the first Supersport practice session on TuesdayImage caption: Ian Hutchinson comes off his Milwaukee Yamaha during the first Supersport practice session on Tuesday 
Press EyeCopyright: Press Eye William Dunlop was fastest in the first Supersport practiceImage caption: William Dunlop was fastest in the first Supersport practice 
Latest PostRider injured
A rider has been airlifted to hospital after a crash in the final lap of the practice session.
The European rider, who was riding a Superstock machine, crashed at Primrose corner, close to the start/finish area of the circuit just four minutes before the session was due to end.
No other bikes were involved.
The rider received lengthy treatment at the scene before being taken by helicopter to hospital in Belfast.
It is not known at this stage if his injuries are life threatening.
Post update
RED FLAG
The red flag is out and, with roads opening again soon, the session is over.
Austrian peaks in Superstock
Horst Saiger from Austria is the surprise name at the top of the Superstock practice times with Michael Rutter second and Stephen Thompson third.
Breaking the limit
Stephen Henderson on Twitter: "Now getting messages from my mobile phone operator that I'm over my data limit. Well worth it. Great coverage.
Amor loving the North West
Keith Amor, a Superstock winner here four years ago, tops the Supertwin times, Ryan Farquhar is second best with Connor Behan third.
Supertwins latest
Falkirk flyer Keith Amor is leading the Supertwins with Ryan Farquhar currently second and Connor Behan third.
Supertwins ready to go
Next up are the Supertwin machines, a class introduced to the North West in 2012. They are four-stroke twin cylinder bikes originally sold for road use with a water cooled engine of up to 650cc.
Superbike sessions ends
Superbike placings: 1) Michael Rutter; 2) Alastair Seeley; 3) Guy Martin; 4) William Dunlop; 5) Martin Jessopp; 6) Josh Brooks
Superbike session
Latest is that Alastair Seeley is setting the Superbike pace, closely followed by Guy Martin, William Dunlop, Michael Rutter and Michael Dunlop.
Pace notes
Marty Tweets from University: "Sitting at my desk in Cambridge watching online trying to look like I'm working hard. If they only knew. Flying over tomorrow so happy days."
Post update
Ian Hutchinson has gone to hospital for a check-up after coming off on the Mill Road section during the Supersport session.
Supersport session ends
William Dunlop tops the unofficial time sheets in the Supersport, Michael Rutter second and Alastair Seeley third.
"I always liked the wee 600 - the bike has been working really well," says Dunlop.
W Dunlop 114.754; Rutter 114.192; Seeley 114.179; L Johnston 114.118; G Johnson 113.828.
Post update
Steve Parrish
BBC motorcycling commentator
Josh Brookes will be happy. I think he's got more laps in already then he managed in all of last year's North West.
Seeley stops
Setback for Alastair Seeley: "We have had to pull in with a bit of an engine problem which is a bit disheartening. I'll have to speak with the boys and see what the problem is."
Update on timings
William Dunlop setting pace
From @northwest200: 15 mins gone of a 35 min session and it is William Dunlop 113.568 ahead of Seeley 112.290 Johnson 112.331 Martin 111.785.
PIT STOP
Rutter has problems
Michael Rutter is back in the pits hoping mechanics can sort out an early problem with his Smiths Triumph machine. "We have one or two things to do, hopefully we can get a few laps in," says the 13-times North West winner.
Post update
Weather watching
A Tweet from the Thruxtonian: The weather is better at your end than here in Barcelona. It's not fair!
Starting soon
The Supersports are on the grid for the first 35-minute practice session
Action delayed
Stephen Watson
BBC Sport NI
Newcomers practice delayed slightly so we are now on air with live NW200 practice at 10.30
Weather outlook
Promising news from @angie_weather on Radio Ulster: "Many places having a better day today, mainly dry and bright with a light on-shore breeze on the north coast."
Tuesday's practice session
Live video streaming of the first practice session for the 2014 North West 200 starts here at 10:15 BST. The Supersport 600 machines will be getting their first run on the 8.9-mile Triangle circuit at 10:30.