Singapore will spend up to 2.25 billion Australian dollars ($1.67 billion) to double the capacity of its military training facilities in northern Australia under a new bilateral deal, Australia's prime minister said Friday.

Malcolm Turnbull said that the investment should be seen in the region as a natural development of a close strategic relationship between the countries.

Full details of the redevelopment of military training areas at Townsville and Shoalwater Bay in Queensland state had yet to be finalized.

Turnbull said up to 14,000 Singaporean troops would train in Australia for up to 18 weeks a year.

The United States has a Marine training hub in the northern Australia center of Darwin and is negotiating to increase air force and navy training in Australia.

The Singaporean military upgrade is part of a comprehensive strategic partnership pact agreed by Turnbull and his Singaporean counterpart Lee Hsien Loong this week.

It builds on a bilateral free-trade agreement that has been in force since 2003.

It includes commitments to open markets and trade, and creates greater opportunities for Australians to trade and work in Singapore, Turnbull said.

Singapore, a city state, has long been attracted to Australia's bombing ranges and military training areas which are among the world's largest.