Greens Senator Sarah Hanson-Young says she has been denied access to the Curtin Detention Centre to visit the 157 Tamil asylum seekers who were held on an Australia Customs ship for almost a month.

Senator Hanson-Young says she had flown to Broome from Adelaide and was on the road to the remote West Australian centre when she was informed that she would not be allowed inside.

She says she has been visiting detention centres for more than six years and this is the first time she has been blocked from entering the Curtin facility.

"I have been there a number of times. I know what it looks like inside. I wanted to speak to the new asylum seekers who are being detained there," she said.

"This is highly suspicious that I have been denied access today.

"This is a political move by the Immigration Minister. What is he hiding? What doesn't he want me to see?"

Senator Hanson-Young, who had publicly flagged the Curtin visit, says she had been liaising with the Immigration Minister Scott Morrison's office over the past few days.

"They knew that the intention was to go in today."

The senator says she wanted to visit the Tamils, who have been the subject of a High Court challenge, to see how they are. It is understood 37 children are part of the group.

"I am extremely concerned about the welfare of the children," she said.

"Today I wanted to speak with them to see how they are faring and to let them know that there are Australians who are really concerned about them, their welfare and what the Government is doing."

In a statement, a spokesperson for Mr Morrison said the minister assessed Senator Hanson-Young's proposed visit.

"When the minister's office became aware of the request the minister sought advice from the Department," the statement said.

"The minister sought advice from his Department on visitor access... and was advised that access would not be appropriate at this time, based on the interests of the good management and safety of the centre."

The spokesperson said requests were considered on a "case by case basis" and said Senator Hanson-Young had been denied access to the Pontville detention centre under the previous Labor government.

On Monday Mr Morrison declared that the Tamils, who set sail from the Indian state of Pondicherry in mid-June, are economic migrants and do not face persecution if they are sent back to India.

Indian consular officials are expected to be at the detention centre within days to help determine the asylum seekers’ identity and residency.

The Indian High Commission has now received an official invitation by Australia to interview the Tamils and both parties are now sorting out arrangements.