Joe Root and Alastair Cook out for ducks as 22 wickets fall at Chelmsford
Yorkshire all out for 50 and Essex make 142 in reply
James Vince falls for five for Hampshire against Notts
Trescothick & Bartlett score 100s for Somerset against Lancashire
Rory Burns hits century for Surrey against Worcestershire
Dawid Malan out for 13 for Middlesex against Sussex
Ollie Robinson takes 7-54 for Sussex, the day's best figures
Surrey 101-3 (40 overs) v Worcestershire
Surrey batsman Rory Burns reaches a very hard fought half-century in the sun at the Oval.
It comes off 123 balls, with six fours, but almost comes at the cost of Ben Foakes' wicket after the Surrey opener hesitated in taking the single.
The pair survive and Burns will be aiming to build on his solid start.
Image source, Getty ImagesYorkshire 50 v Essex 38-3 (14 overs)
Essex batsman Dan Lawrence is showing that it is possible to score runs at Chelmsford today and has so far scored all bar seven of the home side's total, with the help of six fours. At this rate, it won't be long before he has single-handedly surpassed Yorkshire's first-innings total. Ravi Bopara, at the other end, has faced 16 deliveries so far without scoring.
Glamorgan 73-4 (37.3 overs) v Kent
Adam Whitty
BBC Radio Kent
As Will Young might say “I’m going to take this cricketing career, and make it evergreen”.
It would perfectly describe Kent all-rounder Darren Stevens, who once again has made an impact with the ball, four days after celebrating his 42nd birthday.
His probing line and length have turned the tide in this Glamorgan innings. The hosts were 57-0 at lunch, but he struck with his second ball to dismiss Nick Selman and end a defiant opening partnership.
Matt Henry joined in on the fun to send Shaun Marsh packing, before Stevens struck again to dismiss Kiran Carlson and Aneurin Donald on this intriguing opening day.
Surrey 99-3 (37.4 overs) v Worcestershire
A carbon copy wicket for Joe Leach as Ravi Patel tickles the Worcestershire batsman behind to wicketkeeper Ben Cox.
Just the start to the afternoon session the visitors would have wanted.
Leicestershire 110-0 (36 overs) v Durham
Captain Michael Carberry follows partner to 50 with two boundaries in the same over from Chris Rushworth. Carberry's half-century was the quikcer of the two in terms of balls faced - 97 to Horton's 114, and he has nine fours in total.
Rushworth was "accuracy personified" before lunch, according to BBC Radio Leicester commentator Richard Rae, but he has already sent down 14 overs and we're not even half-way through the afternoon session yet.
Derbyshire 318 v Warwickshire 147-2 (43.3 overs)
Image source, Getty ImagesWell played, Chris Wright, who collects a single off Derbyshire fast bowler Duanne Olivier to bring up the 10th first-class fifty of his career. The Warwickshire nightwatchman has been the immovable object so far and has shared an unbroken half-century stand with Ian Bell, who is on 28.
Leicestershire 97-0 (34 overs) v Durham
Paul Horton reaches 50 off 114 balls at the Riverside with a boundary off Chris Rushworth. It's the eighth of his innings so far and Michael Carberry isn't far behind, on 43 not out.
Yorkshire 50 v Essex 12-3 (6.4 overs)
Still it continues at Chelmsford. Ben Coad steams in from round the wicket at Chelmsford and Nick Browne, playing defensively, is bowled between bat and pad. Wonder what the odds are on Yorkshire leading on first innings? Ravi Bopara is the new batsman.
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Surrey 87-2 (31.4 overs) v Worcestershire
Just four balls after lunch and Worcestershire have an important breakthrough.
Captain Joe Leach takes the edge of Scott Borthwick's bat and wicketkeeper Ben Cox takes a simple catch behind the stumps.
Our eight matches are getting under way again...how many wickets will fall at Chelmsford this afternoon?
Here's a pic of the player of the morning - Essex paceman Sam Cook, who took five wickets as Yorkshire were skittled for 50.
Image source, GettyFor several players, this round of matches is not just about helping their respective teams collect points, it's about trying to make a case for inclusion in England's Test squad for the upcoming series against Pakistan.
As this morning's action has shown, no-one is producing the kind of form from which new national selector Ed Smith can draw comfort.
Our esteemed colleague Gary Smee recently took a look at some of the potential candidates and you can read his assessment here.
Middlesex opener Nick Gubbins (pic below) impressed with two centuries in the pre-season North v South contest before succumbing to a hamstring injury. He is now fit again but couldn't manage a big score against Sussex at Hove this morning to give Smith a timely nudge.
Image source, Getty ImagesTweet us at #bbccricket
From MrPayney: "Twelve wickets before lunch?! What on earth is going on at Chelmsford? #bbccricket, external"
From Alex Adams: "An occasional downside to living in the US: When Yorkshire play so badly, they're all out before you even wake up #Yorkshire, external#bbccricket, external"
From Francis Edwards: "Good to see all of the England players doing really well today. Wait, none of them are. I thought they were supposed to be good in England! #bbccricket, external"
From hotelsonametler: "#bbccricket, external can the ecb forcibly press Trescothick into the team for the EngvPak tests. Seems to be the only player scoring runs."
From John Monks: "As another embarrassed Yorkie I have to agree with David (see 1158). Making 50 after choosing to bat first is pitiful. Even if Essex are out for 49...(unlikely), Yorks batting has been sub-standard for too long. Something needs to change #bbccricket, external"
Right, as we take a moment to draw breath after the comings and goings at Chelmsford, here's a bit of BIG county news from yesterday. Bet Surrey fans can't wait to see him.
India captain Virat Kohli agrees a deal to play county cricket for Surrey in June before the Test series against England.
Read MoreDerbyshire 318 v Warwickshire 144-2 - lunch
Nightwatchman Chris Wright has done a fabulous job for Warwickshire, surviving the entire morning session at Edgbaston to reach lunch on 47 not out.
His partnership with Ian Bell (27no) is worth 49 after Derbyshire achieved their only breakthrough so far when Mark Footitt had Will Rhodes caught behind for 50. The visitors, though, still lead by 174.
Nottinghamshire 137-4 (28 overs) v Hampshire - lunch
Image source, Getty ImagesIt has been a see-saw morning at Trent Bridge, with momentum swinging sharply from one direction to the next.
Kyle Abbott and Fidel Edwards struck early to reduce the hosts to 27-3 bringing Patel and overseas batsman Ross Taylor to the crease together.
The fourth-wicket pair shared a 95-run fourth-wicket stand, taking 21 runs off one Edwards over, as they sharply upped the scoring and found the boundary ropes with ease.
Although a mix-up saw Taylor run out three runs short of his half-century, Patel hit his ninth boundary to bring up his fifty - reaching the break unbeaten on 53.
Leicestershire 80-0 v Durham - lunch
Martin Emmerson
BBC Newcastle
The visitors will be more than happy with how things have panned out for them so far today.
They were put in, but Michael Carberry wanted to bat anyway, and after a watchful start he came out of his shell after scoring two from his first 31 balls.
He now has 33 while Paul Horton is on 41 at the other end, but has slowed after setting off at a greater pace than his colleague.
Durham have used five bowlers so far but to no avail. There's not been a chance to mention so far.
Image source, BBC SportIt's a good day for runs and ice cream, but not wickets
Middlesex 81-5 v Sussex - lunch
Adrian Harms
BBC Sussex cricket commentator
A terrific exhibition of controlled seam bowling from Ollie Robinson, who has taken all five wickets to fall and in so doing passed 100 first-class victims.
Middlesex had elected to bat first on a good looking pitch having won the toss but may now be regretting that decision.
Only Steve Eskinazi, with 38, batted with any authority and with Dawid Malan out for 13 just before lunch Sussex will be looking to press home their advantage this afternoon.
Image source, BBC SportGlamorgan 57-0 v Kent - lunch
Adam Whitty
BBC Radio Kent
How on earth are we wicketless here?
Kent have done nothing wrong at all in the Welsh capital, bowling probing lines and lengths to the Glamorgan opening pair.
My voice is almost hoarse from saying "played and missed" so many times in the opening session.
Image source, bbcGlamorgan have been fortunate in the opening session, but their opening pair remain not out
Nick Selman and Jack Murphy have ridden their luck, certainly, but they are still there and will fight on into the afternoon session.
The longer this partnership goes on, the more credit goes to the batsman for their character, if not for the sometimes agonisingly slow pace of the game.
Surrey 83-1 (30 overs) v Worcestershire
It has been a relatively slow and quiet morning in London compared to the rest of the Division One matches.
Surrey batsman Rory Burns has had to dig in, targeting the bad balls - which have been few and far between - reaching 45 off 96 balls at lunch.
The only wicket to fall in the first session was that of Mark Stoneman, with the England opener run out attempting a quick single on a day he was no doubt hoping to impress the national selectors.
Perhaps he will feel a little better if he has a look at the scorecard from Chelmsford over lunch?
Somerset 113-1 v Lancashire - lunch
A successful morning for Somerset at Old Trafford as Marcus Trescothick's unbeaten 54 took them to lunch with a solid foundation for a big score. Matt Renshaw was the only batsman to fall, caught at mid-wicket for 21, while Jimmy Anderson sent down 10 overs for figures of 0-22.
The big story, though, is Anderson's new bleached hairdo. We will publish a photo later if we can.