RCMP say more officers have been called in to help with an illegal blockade at a United States border crossing in southern Alberta, now in its fifth day.

Mounties were prepared to make arrests Tuesday at the Coutts crossing but backed off when there were safety concerns.

Cpl. Curtis Peters says some vehicles left peacefully but others, including tractors, sped through police roadblocks to join the blockade.

He says there was a head-on crash and a person involved then assaulted another person.

Peters also says some protesters have harassed the local mayor and his wife by showing up at their home and taking photos through their windows.

He says the behaviour is not very Canadian.

"The fight is not with the mayor and his wife," Peters told reporters Tuesday night in Coutts.

"They should not be subjected to that kind of harassment in their own home."

Some of those involved in the blockade are protesting mandatory COVID-19 vaccinations for cross-border truck drivers as well as broader public health measures.

Premier Jason Kenney says he also opposes the vaccine mandate for truckers, but protesters should find a lawful way to make their point.

RCMP say they are aware of other blockades happening on highways in and around the Coutts area.

"These blockades will be monitored with the full support of other Alberta law enforcement partners," says a statement.