The Australian Government was aware for at least a week of Vietnam's concerns about too many visitors to Long Tan, the commander of the unit that fought the battle says.

Key points: Commander of Australian forces at Long Tan says he was told about concerns weeks ago

Commander of Australian forces at Long Tan says he was told about concerns weeks ago Julie Bishop says she was only told about concerns two days ago, when the event was cancelled

Julie Bishop says she was only told about concerns two days ago, when the event was cancelled Small groups made it to cross after waiting up to three hours

The Vietnamese Government cancelled Thursday's memorial service for the 50th anniversary of Vietnam War battle, a move which was described as a shock and a "kick in the guts" by Veterans Affairs Minister Dan Tehan.

But the commander of D Company 6RAR, which fought the battle at Long Tan, told the ABC trouble was brewing weeks ago.

"It was mentioned some weeks ago when I was in Canberra that Hanoi was a bit worried about the number of people expected — like 3,000 — and it was all getting too much, too big, getting out of hand," Harry Smith said.

More than 1,000 Australians travelled to Vietnam to attend the anniversary commemorations, but many missed out on paying their respects at the memorial cross at the former battlefield on Thursday.

An agreement between the two Prime Ministers — struck after the cancellation was announced — to allow access to small groups appeared to falter, with Vietnamese police keeping visitors away.

Some Australians did make it to the cross after waiting in queues for up to three hours and were allowed as little as one minute to pay their respects to Australian soldiers who died there.

Other groups gave up after long waits.

Harry Smith (second from right) and his family were turned away from the memorial site. ( ABC News: Bruce Atkinson )

On August 11, the ABC was told by a Vietnamese official at the Ministry of Foreign Affairs that the Long Tan ceremony may be cancelled due to issues between the local government and Australia's Department of Foreign Affairs and Trade (DFAT).

DFAT responded to concerns saying the event would proceed as planned.

Bishop informed of concerns only two days ago

Foreign Minister Julie Bishop denies claims the event was handled poorly by the Australian Government, saying she had spoken with Vietnam's Foreign Minister and Deputy Prime Minister Pham Binh Minh at the end of July about the number of Australians intending to visit Long Tan for the anniversary.

Ms Bishop said she was not informed of concerns about large numbers of visitors until two days ago.

"I spoke with [Foreign Minister Pham Binh Minh] the night before last when we were informed for the first time that the Vietnamese Government intended to cancel the commemorative service," Ms Bishop said.

"They were concerned at the reaction of local people — the sensitivities that the conflict in Vietnam all those years ago still bring to communities in Vietnam."

Ms Bishop said that Vietnam's Prime Minister and Deputy Prime Minister were at pains to say the relationship between Australia and Vietnam "was in the best shape it has been in for 40 years at least".

"On the issue of commemorations relating to the Vietnam War, it is still a very sensitive topic in Vietnam, particularly among the local communities where some of these battles took place," she said.

"While I explained that our veterans were there to pay tribute to all those who sacrificed their lives in the conflict, the emotion was running very deep, and the Vietnamese Government took the action that, as a sovereign government, they are able to do."

Ms Bishop said both she and Prime Minister Malcolm Turnbull spoke to their Vietnamese counterparts and were able to achieve a breakthrough that let hundreds of veterans and families attend a service.

"I think it comes down to the sheer scale and size of what was proposed this year," she said.

"But until the Government gave us formal notice, the other night, we had continued to work closely with the Vietnamese Government about how much it meant to Australian veterans to be in Long Tan at this time."

Many Australian tour groups are again trying to visit the cross today.