Vietnam has cancelled an event marking the 50th anniversary of Australia’s bloodiest battle in the Vietnam War.

The commemoration of the battle of Long Tan was due to be held at a cross marking the site on Thursday.

More than 1,000 Australian veterans and their families have travelled to Vietnam to commemorate the anniversary.

Eighteen Australian soldiers and hundreds of North Vietnamese and Viet Cong fighters died in the battle, deep in southern Vietnam, on 18 August 1966.

Police blocked access to the site, which is on private land, without explanation on Wednesday.

Australian Foreign Minister Julie Bishop confirmed that the Vietnamese government said it will not allow the event to go ahead, although small groups will be allowed access on Thursday.

An official party involving the ambassadors of Australia and New Zealand will lay a wreath at the site.

Australia’s foreign ministry said it was lodging complaints with the Vietnamese government as it was deeply disappointed at this decision, and the manner in which it was taken, so close to the commemoration service taking place.

Australian veterans and their families had planned to attend a ceremony at Long Tan marked by mutual respect to remember and honour the sacrifice of those lost in the Vietnam War from both sides, a statement said.

Local sensitivities are thought to have been behind the sudden decision to stop the event going ahead, although a number of low-key memorial events have been permitted in the past