The 23-year-old Summerhill man crashed into an oncoming truck on Friday and was in a serious condition at the Launceston General Hospital with pelvic injuries.

The two-vehicle crash occurred about 4.40pm near the intersection of Penquite Road and Wentworth Street at Newstead.

As the man is in hospital interstate, Inspector Darren Hopkins said it had slowed down the opportunity to interview him but a file on his alleged armed robberies was being prepared for when he returned.

"He was suspended from driving and his vehicle was unregistered," he said.

"The car in question was also involved in a previous evade a week before on Hoblers Bridge Road."

The man was allegedly involved in three armed robberies last week at BWS, Top Shop and Kmart.

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An armed robbery last Thursday night at Kmart involved a security guard being held at knifepoint before a trolley full of goods was stolen.

The two armed robberies last Friday afternoon, involving a replica firearm, were at the Ravenswood BWS on Castlemain Road and the second at Waverley's Top Shop on the Tasman Highway.

It's alleged the man acted alone on Friday and held a BWS male worker at gunpoint before stealing cash and alcohol.

A short time later a 24-year-old pregnant worker was held at gunpoint at Top Shop and tobacco products and cash was stolen.