China has demanded that Canada release the arrested Huawei executive Meng Wanzhou or face consequences.
Vice Foreign Minister Le Yucheng separately summoned both the US and Canadian ambassadors and lodged a "strong protest" urging her release.
The ministry described Ms Meng's arrest as "extremely nasty".
Ms Meng, Huawei's chief financial officer and daughter of the firm's founder, is accused of breaking US sanctions on Iran.
She was held in Vancouver last Saturday and faces extradition to the US, where she could be jailed for up to 30 years if found guilty.
China insists that she has not violated any laws.
On Friday Ms Meng appeared before a Canadian court, which adjourned a decision on whether or not to allow bail until Monday.
What has China said?
Ms Meng's arrest while she was changing planes in Vancouver last Saturday was a serious breach of her rights, Reuters quoted the foreign ministry as saying.
It "ignored the law" and was "unreasonable", it said.
"China strongly urges the Canadian side to immediately release the detained person… otherwise Canada must accept full responsibility for the serious consequences caused," the statement added.
On Sunday, Le Yucheng made similar demands to the US, warning: "China will respond further depending on US actions."
What happened during Friday's court appearance?
The Supreme Court of British Columbia was told that Ms Meng had used a Huawei subsidiary called Skycom to evade sanctions on Iran between 2009 and 2014.
The court was told that she had publicly misrepresented Skycom as being a separate company.
It heard a Canadian prosecutor say that Ms Meng was accused of "conspiracy to defraud multiple financial institutions".
The prosecutor said she had denied to US bankers any direct connections between Huawei and SkyCom, when in fact "SkyCom is Huawei".
Ms Meng could be a flight risk and thus should be denied bail, he added.
Why was the arrest significant?
The arrest has put further strain on US-China relations. The two countries have been locked in trade disputes, although a 90-day truce had been agreed on Saturday – before news of the arrest came to light on Wednesday.
Huawei is one of the largest telecommunications equipment and services providers in the world, recently passing Apple to become the second-biggest smartphone maker after Samsung.
Canadian Foreign Minister Chrystia Freeland said on Friday that China had been assured that due process was being followed and Ms Meng would have consular access while her case was before the courts.
Ms Freeland reiterated Prime Minister Justin Trudeau's claim that Ms Meng's arrest had "no political involvement".
Who is Meng Wanzhou?
By BBC Monitoring
Meng Wanzhou, 46, joined Huawei as early as 1993, when she began a career at her father's company as a receptionist.
After she graduated with a master's degree in accountancy from the Huazhong University of Science and Technology in 1999, she joined the finance department of Huawei.
She became the company's chief finance officer in 2011 and was promoted to vice-chair a few months before her arrest.
Ms Meng's links to her father, Ren Zhengfei, were not known to the public until a few years ago.
In a practice highly unusual in Chinese tradition, she adopted her family name not from her father but her mother, Meng Jun, who was Mr Ren's first wife.
Does Huawei concern the West?
Some Western governments fear Beijing will gain access to fifth-generation (5G) mobile and other communications networks through Huawei and expand its spying ability, although the firm insists there is no government control.
Japan is expected to ban government use of products made by Huawei and ZTE over cybersecurity concerns, local media reported on Friday. It would follow moves by New Zealand and Australia to block Huawei.
US National Security Adviser John Bolton said his country has had "enormous concerns for years" about the practice of Chinese firms "to use stolen American intellectual property, to engage in forced technology transfers, and to be used as arms of the Chinese government's objectives in terms of information technology in particular".
"Not respecting this particular arrest, but Huawei is one company we've been concerned about," he said.
What are the Iran sanctions?
US President Donald Trump last month reinstated all the US sanctions on Iran that had been removed under a 2015 nuclear deal.
Mr Trump had been fiercely opposed to the deal, which saw Iran limit its controversial nuclear activities in exchange for sanctions relief.
The re-imposed sanctions hit oil exports, shipping and banks – all core parts of Iran's economy.
Although there are some waivers, US Treasury Secretary Steven Mnuchin has said the US will "aggressively" target any firm or organisation "evading our sanctions".