Bidders for German 5G rollout contracts must guarantee the network will be free of foreign state influence, Chancellor Angela Merkel's Christian Democrats agreed on Saturday, stopping short of singling out China's Huawei.

After a heated debate, delegates at the Christian Democratic Union's (CDU) party congress backed a motion stipulating that 5G suppliers must fulfil a "clearly defined security catalogue, which includes the exclusion of influence by a foreign state".

Some CDU lawmakers want China's Huawei, which the United States fears could be used by Beijing for spying, to be excluded from 5G contracts in the country. Merkel wants security standards to be the yardstick, rather than singling out any one company.

The Shenzhen-based company has repeatedly denied the allegations by Washington, which has pressured its allies to shut out Huawei and in May imposed export controls on the company, hobbling its smartphone business and raising questions over whether it can maintain its market lead.

All of the telecoms operators in Germany, which has close trading ties with China, are customers of Huawei and have warned that banning the company would add years of delays and billions of dollars in costs to the launch of 5G networks.