Australia held out for a draw after Jofra Archer and Jack Leach nearly bowled England to an improbable win in the second Ashes Test at Lord's on Sunday.

Australia were 154-6 at the close, having been set a stiff target of 267 in 48 overs when England captain Joe Root declared after lunch on the back of Ben Stokes's unbeaten century.

It seemed the match was destined for a draw, with Australia 132-3 after tea in a Test where five sessions were washed out completely, with rain also delaying Sunday's start by over an hour.

But Australia, who still lead the five-match series 1-0 after their 251-run win at Edgbaston, then lost three wickets for 17 runs to give England renewed hope.

Come the last over, bowled by left-arm spinner Leach, England needed four wickets but Pat Cummins played out three deliveries to secure a draw, with Australia finishing on 154-6.

Fast bowler Archer took 3-32 to finish with five wickets on his Test debut, with Leach returning figures of 3-37.

Australia's Steve Smith had to sit out Sunday's play with concussion suffered when hit by a bouncer from Test debutant Archer during his 92 on Saturday — the first time this series he had been out for under a hundred.

Given the short turnaround, Smith could now miss the third Test in Leeds starting on Thursday.

His absence would be a huge blow to Australia, bidding for their first Ashes series win in England in 18 years, given he made 144 and 142 at Edgbaston in his first Test since completing a 12-month ban for his role in a ball-tampering scandal in South Africa.

Labuschagne hit on helmet

Archer also struck Smith's replacement Marnus Labuschagne — cricket's first concussion substitute — on the grille of his helmet on Sunday.

But Labuschagne responded by top-scoring with 59.

World Cup winner Archer took two for two in seven balls on Sunday.

David Warner's miserable series continued when, on five, he edged Archer to Rory Burns in the slips.

Australia were 19-2 when Usman Khawaja was caught behind off a fine Archer ball just outside off stump for two.

Archer's second delivery to Labuschagne, was a 91.6 mph bouncer that him flush on the grille.

But Labuschagne eventually resumed his innings and later bravely drove Archer down the ground for four — one of seven he hit in an admirable 89-ball fifty.

The first over after tea saw struggling opener Cameron Bancroft (16) plumb lbw to a ball that kept low from Leach, with Australia in trouble at 47-3.

It seemed any hope of an England win had disappeared when Jason Roy dropped a routine chance at second slip to reprieve Travis Head on 22. Head finished on 42 not out.

But Labuschagne fell when his sweep off Leach deflected off Jos Buttler at short leg before looping to Root, diving forward at midwicket.

The onfield 'soft signal' was out and third umpire Joel Wilson eventually upheld that verdict to the disgust of Labuschagne, who exchanged words with Root on his way into the pavilion.

Leach then had Matthew Wade (one) taken at short leg before Joe Denly held a sensational diving left-handed catch at midwicket to dismiss Tim Paine following the Australia captain's full-blooded pull off Archer.

But with the natural light fading, the umpires appeared to instruct Root not to bowl Archer even though the floodlights were on -- effectively depriving the paceman of two overs.

Earlier man-of-the-match Stokes scored 115 not out before Root declared England's second innings on 258-5.

Stokes slog-swept off-spinner Nathan Lyon for two sixes in as many deliveries on the way to a 160-ball century, his seventh in Tests and second against Australia.