Asylum seeker boat near Christmas Island

Refugee activists are urging the federal government to help a boatload of Tamil asylum seekers heading for Christmas island.

Refugee Action Coalition spokesman Ian Rintoul says they're extremely concerned the government may attempt to divert the asylum seekers or leave assistance until it's too late.

Mr Rintoul says the boat, carrying 153 asylum seekers, including almost 70 women and children, is said to have sprung an oil leak.

The government's refused to comment for operational reasons but Mr Rintoul says people on the boat have made contact with Australian maritime rescue authorities and are asking for help.