"The branch is to remain closed until further notice, following an earthquake assessment report. We're working closely with the mall's property managers on further investigations.
"The health and safety of our staff and customers is paramount. We understand this closure may cause inconvenience to our LynnMall customers and we apologise for this," a Westpac spokeswoman said.
Westpac staff had temporarily moved to nearby branches at Blockhouse Bay, St Lukes and Mt Roskill "and we welcome our LynnMall customers there and to any other convenient Westpac branch locations".
NZX-listed Kiwi Property owns the shopping centre and its chief executive Chris Gudgeon acknowledged issues and the bank's closures but he said ASB remained open at LynnMall.
"We have proactively undertaken a seismic assessment on parts of LynnMall, which we undertook due to their age - LynnMall first opened in 1963 and various parts are now more than 50 years old - and the fact that the mall has been progressively built over many decades to different codes. Even though LynnMall sits within a low seismic risk area, a seismic assessment was a prudent exercise.
"Certain parts of the centre have, been assessed by our structural engineers as being earthquake-prone," Gudgeon said.
Auckland is a low-risk seismic risk area, and the Government had allowed property owners a 35-year timeframe to strengthen buildings, he noted.
"Our plan is to undertake the necessary strengthening works as soon as practicable and in accordance with our legal obligations, while keeping the affected areas operational. We have not required any tenants to close, albeit two banking tenants have made their own decision to close, while a third, ASB, continues to trade," he said.
An ASB spokeswoman said: "We take the safety of our customers and staff very seriously.
"ASB has a robust earthquake policy, which reflects regional risk. The branch at LynnMall has been assessed according to this policy. We work closely with the mall's landlord Kiwi Property."
Gudgeon said the mall had 141 tenants "and the two tenants who have chosen to close represent 1.5 per cent of the centre's net lettable area".
"We take our role as a responsible landlord very seriously. Since 2011, we have undertaken earthquake strengthening works at a cost of over $120 million for our buildings outside of Auckland."
Kiwi had focused on areas of high and moderate seismic risk, progressively working its way up from Christchurch to Wellington, Porirua, Palmerston North and Hamilton.
"Our programme of strengthening work will be completed within a fraction of the time allowed by the Government under the Building Act. Generally, we have managed to complete this work while allowing our tenant customers to continue business operations.
"As part of this strengthening programme, we will now be focused on those parts of LynnMall that need attention," Gudgeon said.
"We know from experience that designing, consenting and programming these works takes time and needs to be undertaken with care to allow continuous business operations for our tenant customers. Tenants who are affected have been notified of the results of the engineering assessment, and it is business as usual for LynnMall, apart from two tenants who have chosen to close."
LynnMall was valued last year at $269m and this year at $271m, Kiwi's annual report showed.
LYNNMALL
• First NZ enclosed shopping centre, opened 1963
• 8.4 million visits each year
• More than 100 specialty stores
